ACT Math : Algebra

Study concepts, example questions & explanations for ACT Math

varsity tutors app store varsity tutors android store varsity tutors ibooks store

Example Questions

Example Question #2 : Quadratic Equations

64x2 + 24x - 10 = 0

Solve for x

Possible Answers:
1/4 and -3/4
1/4 and -5/8
-1/4 and 3/4
1/4 and 5/8
-1/4 and -5/8
Correct answer: 1/4 and -5/8
Explanation:

64x2 + 24x - 10 = 0

Factor the equation:

(8x + 5)(8x – 2) = 0

Set each side equal to zero

(8x + 5) = 0

x = -5/8

(8x – 2) = 0

x = 2/8 = 1/4

Example Question #1 : How To Factor The Quadratic Equation

Which of the following is a root of the function f(x)=2x^2-7x-4 ?

Possible Answers:

x = -2

x = \frac{1}{4}

x = -\frac {1}{2}

x = \frac{1}{2}

x = -4

Correct answer:

x = -\frac {1}{2}

Explanation:

The roots of a function are the x intercepts of the function. Whenever a function passes through a point on the x-axis, the value of the function is zero. In other words, to find the roots of a function, we must set the function equal to zero and solve for the possible values of x.

f(x)=2x^2-7x-4 = 0

This is a quadratic trinomial. Let's see if we can factor it. (We could use the quadratic formula, but it's easier to factor when we can.)

Because the coefficient in front of the x^2 is not equal to 1, we need to multiply this coefficient by the constant, which is –4. When we mutiply 2 and –4, we get –8. We must now think of two numbers that will multiply to give us –8, but will add to give us –7 (the coefficient in front of the x term). Those two numbers which multiply to give –8 and add to give –7 are –8 and 1. We will now rewrite –7x as –8x + x.

2x^2-7x-4=2x^2-8x+x-4=0

We will then group the first two terms and the last two terms.

(2x^2-8x)+(x-4)=0

We will next factor out a 2x from the first two terms.

(2x^2-8x)+(x-4)=2x(x-4)+1(x-4)=(2x+1)(x-4)=0

Thus, when factored, the original equation becomes (2+ 1)(x – 4) = 0.

We now set each factor equal to zero and solve for x.

2x + 1 = 0

Subtract 1 from both sides.

2x = –1

Divide both sides by 2.

x=-\frac{1}{2}

Now, we set x – 4 equal to 0.

x – 4 = 0

Add 4 to both sides.

x = 4

The roots of f(x) occur where x = -\frac{1}{2},4.

The answer is therefore  x = -\frac {1}{2}.

Example Question #5 : Quadratic Equations

36x2 -12x - 15 = 0

Solve for x

Possible Answers:

1/2 and 5/6

-1/2 and 5/6

1/2 and 1/3

1/2 and -1/3

-1/2 and -5/6

Correct answer:

-1/2 and 5/6

Explanation:

36x2 - 12x - 15 = 0

Factor the equation:

(6x + 3)(6x - 5) = 0

Set each side equal to zero

6x + 3 = 0

x = -3/6 = -1/2

6x – 5 = 0

x = 5/6

Example Question #3 : Quadratic Equation

What is the sum of all the values of  that satisfy:

Possible Answers:

Correct answer:

Explanation:

With quadratic equations, always begin by getting it into standard form:

Therefore, take our equation:

And rewrite it as:

You could use the quadratic formula to solve this problem.  However, it is possible to factor this if you are careful.  Factored, the equation can be rewritten as:

Now, either one of the groups on the left could be  and the whole equation would be .  Therefore, you set up each as a separate equation and solve for :

OR

The sum of these values is:

Example Question #11 : Quadratic Equations

What are the two solutions to the following quadratic equation? 

Possible Answers:

 and 

 and 

 and 

 and 

 and 

Correct answer:

 and 

Explanation:

The equation can be factored.

First pull out a common factor of three from each term.

 .

Now, find the factors of the constant term that when added together result in the middle term.

The roots are what values will make the equation equal .  

Therefore, the answers are  and 

Example Question #541 : Algebra

What is the sum of the two solutions of the equation x2 + 5x – 24 = 0?

 

Possible Answers:

24/5

-24

3

-24/5

-5

Correct answer:

-5

Explanation:

First you must find the solutions to the equation. This can be done either by using the quadratic formula or by simply finding two numbers whose sum is 5 and whose product is -24 and factoring the equation into (x + 8)(x – 3) = 0. The solutions to the equation are therefore -8 and 3, giving a sum of -5.

 

 

 

Example Question #542 : Algebra

The height of a ball (in feet) after it is thrown in the air is given by the expression

s(t) = –t2 + 4t

where t is time in seconds. The ball is thrown from ground level at t = 0. How many seconds will pass before the ball reaches the ground again?

Possible Answers:

4

10

6

2

8

Correct answer:

4

Explanation:

Notice that when the ball is at ground level, the height is zero. Setting (t) equal to zero and solving for t will then give the times when the ball is at the ground.

–t2 + 4t =0

t(4 – t) = 0

t = 0, t = 4

The ball returns to the ground after 4 seconds.

Example Question #12 : Quadratic Equations

Two positive consecutive multiples of 3 have a product of 180.  What is the sum of the two numbers?

Possible Answers:

Correct answer:

Explanation:

Define varables as  = the first number and  = the second number.  The product of the numbers is .  Solve the resulting quadratic equation x^{2} + 3x - 180 = 0 by factoring and setting each factor to zero.  The numbers are 12 and 15 and the sum is 27.

Example Question #13 : Quadratic Equations

Given the equation: .

What is the product of the solutions of the quadratic equation?

Possible Answers:

Correct answer:

Explanation:

We are initially presented with a quadratic equation, . To begin we must factor this equation.

The multiples of 15 are (15 and 1) and (3 and 5). The only multiples that add or subtract to  are 3 and 5. Hence we use these as our binomial numbers. . We must now decide on the signs. Because we need to add or subtract 5 and 3 to get to , both signs must be negative: .

From this point we need to switch gears to find solutions to the equation. What numbers would make this equation equal 0?

At this point split the equation into two parts.

 and  and solve.

 and . Both of these numbers inserted into the original equation will produce a result of 0.

Now the question itself is asking for the product of the solutions to the equation, or , which equals 15, therefore 15 is our answer. 

Example Question #14 : Quadratic Equations

If x^2=25 and y^2=81, what is the greatest value that (x-y)^2 can have?

Possible Answers:

16

100

25

196

81

Correct answer:

196

Explanation:

Solving for x yields -5 and5. Solving for y yields -9 and 9.

The greatest difference between these two numbers is 14, and 14 squared is 196.

Learning Tools by Varsity Tutors