SAT Math : Simplifying Expressions

Study concepts, example questions & explanations for SAT Math

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Example Questions

Example Question #773 : Algebra

If a, b, and c are all negative numbers such that ab = 5, bc = 4, and ac = 20, then what is abc? 

Possible Answers:

–20

–400

400

20

100

Correct answer:

–20

Explanation:

If we were to multiply ab, bc, and ac together, we would get (ab)(bc)(ac) = a2b2c2 = (abc)2. If we were then to take the square-root of (abc)2, we would get abc, which is what the question asks us to find.

We know that ab = 4, bc = 5, and ac = 20. Thus (ab)(bc)(ac) = (4)(5)(20) = 400.

(ab)(bc)(ac) = a2b2c2 = 400.

(abc)2 = 400

abc = +√400 or –√400

abc = 20 or –20.

However, we are told that a, b, and c are all negative numbers, so the product of all three must be negative. Therefore, abc must be -20.

The answer is –20. 

Example Question #12 : Simplifying Expressions

Which of the following expressions is equal to 2√8 + 5√8 – 4√16?

Possible Answers:

2√2

14√2 – 16

–√8

26√2

7√8 – 32

Correct answer:

14√2 – 16

Explanation:
  • 2√8 = 2√4 * √2 = 2 * 2√2 = 4√2
  • 5√8 = 5√4 * √2 = 5 * 2√2 = 10√2
  • 4√16 = 4 * 4 = 16

 4√2 + 10√2 = 14√2

14√2 – 16

Example Question #13 : Simplifying Expressions

Simplify the following expression:

2x(x2 + 4ax – 3a2) – 4a2(4x + 3a)

Possible Answers:

–12a3 – 14a2x + 2x3

–12a– 14ax2 + 2x3

12a– 16a2x + 8ax2 + 2x3

–12a– 22a2x + 8ax2 + 2x3

12a– 22a2x + 8ax2 + 2x3

Correct answer:

–12a– 22a2x + 8ax2 + 2x3

Explanation:

Begin by distributing each part:

2x(x2 + 4ax – 3a2) = 2x * x2 + 2x * 4ax – 2x * 3a2 = 2x3 + 8ax2 – 6a2x

The second:

–4a2(4x + 3a) = –16a2x – 12a3

Now, combine these:

2x3 + 8ax2 – 6a2x – 16a2x – 12a3

The only common terms are those with a2x; therefore, this reduces to

2x3 + 8ax2 – 22a2x – 12a3

This is the same as the given answer:

–12a– 22a2x + 8ax2 + 2x3

Example Question #11 : Simplifying Expressions

The square of the sum of p and q is equal to the product of n and the positive difference between j and k. Which of the following algebraic equations could be used to relate p, q, n, j, and k?

Possible Answers:

(p + q)2 = n • |j + k|

(p + q)2 = n(k – j)

(p + q)2 = n • |k – j|

p2 + q2 = n • |j – k|

p2 + q2 = n • |j + k|

Correct answer:

(p + q)2 = n • |k – j|

Explanation:

In order to translate words into symbols and algebraic expressions, we must take each piece of the statement one at a time. First, the problem mentions the square of the sum of p and q. This means we must first find the sum of p and q, and then find the square of this quantity. The sum of p and q can be represented by p + q. The square of this expression would be written as (p + q)2

Where the sentence says "is equal to," we must put an equal sign. This means we can put an equal sign after (p + q)2. So our sentence is now as follows:

(p + q)

Now, let's look at the last part of the sentence to see what should go on the right of the equal sign. 

We must write an expression to represent the product of n and the positive difference of j and k. A product requires multiplication. So we are going to multiply n by the positive difference of j and k.

The difference of j and k could be represented as either j – k or as k – j. However, the statement calls for the positive difference. We don't know whether j or k is larger, so we don't know if j – k is positive, or if k – j is positive. The only way to ensure that we get a positive result is to take the absolute value of the difference. In other words, we can write the positive difference as either |j – k| or as |k – j|, because the absolute value will ensure that we yield a positive value. Also, because, in general, |a – b| = |b – a|, it doesn't matter whether or not we represent the positive difference of j and k as |j – k| or as |k – j|.

Now, let us finish writing the product of n and the positive difference of j and k. Because a product requires multiplication, we must multiply n by the positive difference of j and k, which we just determined can be either |j – k| or |k – j|. Thus, symbolically, we can write this as n • |j – k| or n • |k – j|.

Finally, when we put all of the pieces together, the equation becomes:

(p + q)= n • |k – j|

The answer is (p + q)= n • |k – j|.

Example Question #11 : Simplifying Expressions

If x = 2t + 3 and y = –100t2, find the value of y in terms of x.

Possible Answers:

y/50 + 3

25(x – 3)2

–25(x + 3)2

–25(x – 3)2

–y/50 + 3

Correct answer:

–25(x – 3)2

Explanation:

Since y = –100t2 (in terms of t), we would like to replace the expression t with something in terms of x. Solving the first equation for t, we see:

x = 2t + 3

x – 3 = 2t

(x – 3)/2 = t

Therefore, y = –100((x – 3)/2)2 = –100(x – 3)2/4 = –25(x – 3)2

Example Question #12 : Simplifying Expressions

If one half the value of three more than x is twice the value of three less than y, what is the value of y in terms of x?

Possible Answers:

(x + 15)/4

x/4 + 3

4x

4x + 6

4x – 15

Correct answer:

(x + 15)/4

Explanation:

"one half the value of three more than x" is the same as 1/2(x + 3)

"is" is the same as "="

"twice the value of three less than y" is the same as 2(y – 3)

So 1/2(x + 3) = 2(y – 3).

Multiply both sides by 2: x + 3 = 4(y – 3)

Distribute: x + 3 = 4y – 12

Add 12 to both sides: x + 15 = 4y

Divide both sides by 4: (x + 15)/4 = y

Example Question #17 : Simplifying Expressions

If x2 – (y – z)2 = 40, and x – y + z = 10, then what is the value of x?

Possible Answers:

4

cannot be determined

7

30

50

Correct answer:

7

Explanation:

The problem states that x2 – (y – z)2 = 40, and x – y + z = 10. Because we are asked to find x, we need to find an equation for y and z in terms of x. This will be much easier to do in the second equation than in the first. Let's try to get the y and z terms by themselves, and then put everything else on the other side.

x – y + z = 10

Subtract x from both sides.

–y + z = 10 – x

Notice, that if we were to multiply –y + z by negative one, we would get y – z, which appears in our first equation. Let's multiply both sides by –1. 

–1(–y + z) = –1(10 – x)

Distribute on both sides.

y – z = –10 + x = x – 10

In short, we see that y – z = x – 10. Thus, we can substitute x – 10 into the first equation in place of y – z.

x2 – (y – z)2 = 40

x2 – (x – 10)2 = 40

Next, we will simplify.

x2 – (x – 10)(x – 10) = 40

Use the FOIL technique to find (x – 10)(x – 10).

According to the FOIL method, we find the product of the first terms of the binomials, then the outer terms, then the inner binomials, then the last terms, and then we add these four products together.

Applying the FOIL technique, (x – 10)(x – 10) = x(x) + x(–10) + –10(x) + (–10)(–10) = x2 – 10x – 10x + 100. Let's now replace (x – 10)(x – 10) with x2 – 10x – 10x + 100.

x2 – (x2 – 10x – 10x + 100) = 40

Distribute the –1.

x2 – x2 + 10x + 10x – 100 = 40

Combine like terms.

20x – 100 = 40

Add 100 to both sides.

20x = 140

Divide both sides by 20.

x = 7.

The answer is 7.

Example Question #18 : Simplifying Expressions

If f(x) is a function such that f(x) = f(–x) for every value of x in its domain, then f(x) is classified as an even function. All of the following are even functions EXCEPT:

Possible Answers:

g(x) = 4 + 3x2 + x–2

g(x) = x2(x4 – 1)–1

g(x) = 2x(x – 1)2

g(x) = 4x4 – x6

g(x) = (4x – 1)(4x + 1)

Correct answer:

g(x) = 2x(x – 1)2

Explanation:

Let's look at the function g(x) = (4x – 1)(4x + 1). We want to find g(–x) and see if that equals g(x).

g(–x) = (4(–x) – 1)(4(–x) + 1)

= (–4x – 1)(–4x + 1)

We can factor out a –1 from both binomials.

(–4x – 1)(–4x + 1) = (–1)(4x + 1)(–1)(4x – 1)

Notice that we could arrange this as (–1)(–1)(4x + 1)(4x – 1). And because (–1)(–1) = 1, we would be left with (4x + 1)(4x – 1), which is our original g(x).

Therefore, g(x) = (4x – 1)(4x + 1) is indeed an even function.

Next, we will examine g(x) = 4x4 – x6

g(–x) = 4(–x)4 – (–x)6

Because of the property of exponents which states that (ab)c = acbc, we can rewrite the above expressions as:

4(–1)4x4 – (–1)6(x6)

Whenever -1 is raised to an even-valued exponent, the result is positive one.  For example, (–1)4 = (–1)(–1)(–1)(–1) = 1. Let's go back to simplifying f(–x).

g(–x) = 4(–1)4x4 – (–1)6(x6) = 4(1)x4 – (1)x6 = 4x4 – x6 = g(x).

Thus, 4x4 – x6 is an even function.

Next, let's examine g(x) = 4 + 3x2 + x–2.

g(–x) = 4 + 3(–x)2 + (–x)–2

= 4 + 3(–1)2x2 + (–1)–2x–2 = 4 + 3x2 + x–2 = g(x). This function is even as well.

Now, let's look at g(x) = x2(x4 – 1)–1.

g(–x) = (–x)2((–x)4 – 1)–1

= x2(x4 – 1) = g(x)

Finally, we will analyze g(x) = 2x(x – 1)2.

g(–x) = 2(–x)(–x – 1)2 = –2x(–1)2(x + 1)2 = –2x(x + 1)2, which doesn't equal 2x(x – 1)2 .

In this case, g(–x) is not the same as g(x), so this function cannot be even.

The answer is g(x) = 2x(x – 1)2.

Example Question #3 : How To Do Distance Problems

Gary is the getaway driver in a bank robbery. When Gary leaves the bank at 3 PM, he is going 60 mph, but the police officers are 10 miles behind traveling at 80 mph. When will the officers catch up to Gary?

Possible Answers:

3:10 PM

3:30 PM

5:00 PM

4:45 PM

4:00 PM

Correct answer:

3:30 PM

Explanation:

Traveling 20 mph faster than Gary, it will take the officers 30 minutes to catch up to Gary. The answer is 3:30 PM.

Example Question #19 : Simplifying Expressions

Let f(x) be a function, and let a and b represent any numbers belonging to the domain of f(x). If f(b) = f(a) + f(b) for all of the possible values of a and b, then f(x) is considered "special." Which of the following functions is special?

Possible Answers:

f(x) = |x|

f(x) = (+ 1)2 – x2

f(x) = x2

f(x) = 2x

f(x) = (+ 1)2 – (x – 1)2

Correct answer:

f(x) = (+ 1)2 – (x – 1)2

Explanation:

In order to solve this problem, we need to look at each function separately and then derive expressions for f(b), f(a), and f(b). Then, we need to see whether f(b) = f(a) + f(b).

Let's start with the function 2x.

f(b) = 2(a+b)

Using our property of exponents that xyxz = xy+z, we can rewrite 2a+b.

f(b) = 2(a+b) = 2a2b

Now, let's derive an expression for f(a) + f(b).

f(a) = 2a, and f(b) = 2b. Thus, f(a) + f(b) = 2a + 2b

Let's compare f(b) and f(a) + f(b).

Does 2a2b = 2a + 2b? It might, but not for every value of a and b. For example, let a and b both equal 0.

2020 = 1(1) = 1

2+ 20 = 1 + 1 = 2

If a and b are both zero, then it isn't true that f(b) = f(a) + f(b). Thus, f(x) = 2x isn't special.

Next, let's examine the function f(x) = |x|.

f(b) = |b|

f(a) + f(b) = |a| + |b|

|b| doesn't always equal |a| + |b|. For example, if a = –1 and b = 1, then |b| = |–1 + 1| = 0, while f(a) + f(b) = |–1| + |1| = 1 + 1 = 2. Because f(b) is not always going to equal f(a) + f(b), the function f(x) = |x| isn't special.

The next function we can analyze is f(x) = x2.

f(b) = (b)2 = a2 +2ab + b2

f(a) + f(b) = a2 + b2

a2 + 2ab + b2 doesn't always equal a2 + b2 . Thus, f(x) = x2 isn't special.

The next function is f(x) = (+ 1)2 – x2. We can simplify f(x) a little bit to make it easier to work with.

f(x) = (x + 1)2 – x2 = (x2 + 2x + 1) – x2 = 2x + 1.

f(x) = 2x + 1.

f(b) = 2(b) + 1 = 2a + 2b + 1

f(a) + f(b) = (2a + 1) + (2b + 1) = 2a + 2b + 2

2a + 2b + 1 doesn't equal 2a + 2b + 2, so this isn't a special function either.

 

This means that f(x) = (+ 1)2 – (x – 1)2 must be special. Let's see why.

First, let's simplify f(x).

f(x) = (+ 1)2 – (x – 1)2 = (x2 + 2x + 1) – (x2 – 2x + 1) = x2 + 2x + 1 – x2 + 2x – 1 = 4x.

f(x) = 4x.

f(b) = 4(b) = 4a + 4b

f(a) + f(b) = 4a + 4b

4a + 4b is always equal to 4a + 4b. This means that the function is special.

The answer is f(x) = (+ 1)2 – (x – 1)2 .

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