SAT II Math I : SAT Subject Test in Math I

Study concepts, example questions & explanations for SAT II Math I

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Example Questions

Example Question #41 : Number Theory

Which of the following choices gives a sixth root of sixty-four?

Possible Answers:

\(\displaystyle 1 + i \sqrt{3 }\)

\(\displaystyle 1 - i \sqrt{3 }\)

All of these

\(\displaystyle -1 - i \sqrt{3 }\)

\(\displaystyle -1 + i \sqrt{3 }\)

Correct answer:

All of these

Explanation:

Let \(\displaystyle x\) be a sixth root of 64. The question is to find a solution of the equation

\(\displaystyle x^{6} = 64\).

Subtracting 64 from both sides, this equation becomes

\(\displaystyle x^{6} - 64= 0\)

64 is a perfect square (of 8) The binomial at left can be factored first as the difference of two squares:

\(\displaystyle (x^{3} ) ^{2}- 8 ^{2}= 0\)

\(\displaystyle ( x^{3} + 8 )( x^{3} - 8 )= 0\)

8 is a perfect cube (of 2), so the two binomials can be factored as the sum and difference, respectively, of two cubes:

\(\displaystyle x^{3} + 8 = x^{3}+ 2 ^{3} = (x+2) (x^{2}- x \cdot 2 + 2 ^{2}) = (x+2) (x^{2}-2x+4)\)

\(\displaystyle x^{3} - 8 = x^{3}+ 2 ^{3} = (x-2) (x^{2}+x \cdot 2 + 2 ^{2}) = (x-2) (x^{2}+2x+4)\)

The equation therefore becomes 

\(\displaystyle (x+2) (x^{2}-2x+4) (x-2) (x^{2}+2x+4) = 0\).

By the Zero Product Principle, one of these factors must be equal to 0.

If \(\displaystyle x+ 2 = 0\), then \(\displaystyle x = -2\); if \(\displaystyle x-2 = 0\), then \(\displaystyle x = 2\). Therefore, \(\displaystyle -2\) and 2 are sixth roots of 64. However, these are not choices, so we examine the other polynomials for their zeroes.

 

If \(\displaystyle x^{2}-2x+4 = 0\), then, setting \(\displaystyle a= 1, b= -2, c= 4\) in the following quadratic formula:

\(\displaystyle x = \frac{-b \pm \sqrt{b^{2}-4ac}}{2a}\)

\(\displaystyle = \frac{- (-2) \pm \sqrt{ (-2)^{2}-4(1)(4)}}{2(1)}\)

\(\displaystyle = \frac{2 \pm \sqrt{ 4 - 16 }}{2}\)

\(\displaystyle = \frac{2 \pm \sqrt{ -12 }}{2}\)

\(\displaystyle = \frac{2 \pm\sqrt{4 } \cdot \sqrt{ -1} \cdot \sqrt{3 }}{2}\)

\(\displaystyle = \frac{2 \pm 2i \sqrt{3 }}{2}\)

\(\displaystyle =1 \pm i \sqrt{3 }\)

 

If \(\displaystyle x^{2}+2x+4= 0\), then, setting \(\displaystyle a= 1, b=2, c= 4\) in the quadratic formula:

\(\displaystyle x = \frac{-b \pm \sqrt{b^{2}-4ac}}{2a}\)

\(\displaystyle = \frac{- 2 \pm \sqrt{ 2^{2}-4(1)(4)}}{2(1)}\)

\(\displaystyle = \frac{-2 \pm \sqrt{ 4 - 16 }}{2}\)

\(\displaystyle = \frac{-2 \pm \sqrt{ -12 }}{2}\)

\(\displaystyle = \frac{-2 \pm\sqrt{4 } \cdot \sqrt{ -1} \cdot \sqrt{3 }}{2}\)

\(\displaystyle = \frac{-2 \pm 2i \sqrt{3 }}{2}\)

\(\displaystyle =-1 \pm i \sqrt{3 }\)

 

Therefore, the set of sixth roots of 64 is 

\(\displaystyle \left \{ -4, 4,-1 - i \sqrt{3 }, -1 + i \sqrt{3 } ,1 - i \sqrt{3 }, 1 + i \sqrt{3 } \right \}\).

All four choices appear in this set.

Example Question #42 : Number Theory

Let \(\displaystyle x\) and \(\displaystyle y\) be complex numbers. \(\displaystyle \overline{x}\) and \(\displaystyle \overline{y}\) denote their complex conjugates. 

\(\displaystyle xy = 13+ 7i\)

\(\displaystyle x= 4 - 7 i\)

Evaluate \(\displaystyle \overline{x} \cdot \overline{y}\).

Possible Answers:

\(\displaystyle 7 - 13i\)

\(\displaystyle 7 + 13i\)

\(\displaystyle -13 + 7i\)

None of these

\(\displaystyle -13 - 7i\)

Correct answer:

None of these

Explanation:

Knowing the actual values of \(\displaystyle x\) and \(\displaystyle y\)  is not necessary to solve this problem. The product of the complex conjugates of two numbers is equal to the complex conjugate of the product of the numbers; that is,

 \(\displaystyle \overline{x} \cdot \overline{y} = \overline{xy}\)

\(\displaystyle xy = 13+ 7i\), so \(\displaystyle \overline{xy }= 13- 7i\), and

\(\displaystyle \overline{x} \cdot \overline{y} =13- 7i\),

which is not among the choices.

Example Question #43 : Number Theory

\(\displaystyle \overline{x}\) denotes the complex conjugate of \(\displaystyle x\).

If \(\displaystyle x = 5 + 2i\), then evaluate \(\displaystyle x^{3} \cdot \overline{x} ^{3}\).

Possible Answers:

None of these

\(\displaystyle 24, 389\)

\(\displaystyle 1,000\)

\(\displaystyle -64\)

\(\displaystyle 9,261\)

Correct answer:

\(\displaystyle 24, 389\)

Explanation:

Applying the Power of a Product Rule:

\(\displaystyle x^{3} \cdot \overline{x} ^{3}=(x \overline{x})^{3}\)

The complex conjugate of an imaginary number \(\displaystyle x = a+ bi\) is \(\displaystyle \overline{x} = a - bi\); the product of the two is 

\(\displaystyle x \overline{x} = a^{2} + b^{2}\)

\(\displaystyle x = 5 + 2i\), so, setting \(\displaystyle a = 5 , b = 2\) in the above pattern:

\(\displaystyle x \overline{x} = 5^{2} + 2^{2} = 25 + 4 = 29\)

Consequently, 

\(\displaystyle x^{3} \cdot \overline{x} ^{3}=(x \overline{x})^{3} = 29 ^{3}= 24, 389\)

Example Question #83 : Real Numbers

Evaluate the expression.

\(\displaystyle \small (3+4)^2+(\frac{3+5}{2})+6\div 2\)

Possible Answers:

\(\displaystyle 33\)

\(\displaystyle 56\)

\(\displaystyle 60\)

\(\displaystyle 29\)

Correct answer:

\(\displaystyle 56\)

Explanation:

Follow the correct order of operations: parenthenses, exponents, multiplication, division, addition, subtraction.

\(\displaystyle \small (3+4)^2+(\frac{3+5}{2})+6\div 2\)

First, evaluate any terms in parenthesis.

\(\displaystyle (7)^2+(\frac{8}{2})+6\div 2\)

\(\displaystyle 7^2+4+6\div 2\)

Next, evaluate the exponent.

\(\displaystyle \small 49+4+6\div2\)

Divide.

\(\displaystyle \small 49+4+3\)

Finally, add.

\(\displaystyle \small 49+4+3=56\)

Example Question #1 : Mathematical Relationships

Evalute the expression:

\(\displaystyle \left (\frac{3*2}{6}\right)+8^2-4*6+5\)

Possible Answers:

\(\displaystyle \small 21\)

\(\displaystyle 46\)

\(\displaystyle \small 64\)

\(\displaystyle \small 366\)

Correct answer:

\(\displaystyle 46\)

Explanation:

Follow the correct order of operations: parentheses, exponents, multiplication, division, addition, subtraction. (This is typically abbreviated as PEMDAS. Note that both multiplication and division, and addition and subtraction, are equal to each other in terms of rank, so when both are present, solving the equation proceeds from left to right).

First, simplify anything in parentheses.

\(\displaystyle \left(\frac{6}{6}\right)+8^2-4*6+5\)

\(\displaystyle \small 1+8^2-4*6+5\)

Next, simplify any terms with exponents.

\(\displaystyle \small 1+64-4*6+5\)

Now, perform multiplication.

\(\displaystyle \small 1+64-24+5\)

Since all we are left with is addition and subtraction, we perform simplification from left to right.

\(\displaystyle \small \small 65-24+5 = 41+5=46\)

Thus, our answer is:

\(\displaystyle \small \small 46\)

Example Question #2 : Mathematical Relationships

Add in modulo 7:

\(\displaystyle 5 + 4 + 6 + 2\)

Possible Answers:

\(\displaystyle 3\)

\(\displaystyle 4\)

\(\displaystyle 2\)

\(\displaystyle 5\)

\(\displaystyle 6\)

Correct answer:

\(\displaystyle 3\)

Explanation:

In modulo 7 arithmetic, a number is congruent to the remainder of its division by 7. 

Therefore, since \(\displaystyle 5 + 4 + 6 + 2 = 17\) and \(\displaystyle 17 \div 7 = 2 \textrm{ R }3\),

\(\displaystyle 5 + 4 + 6 + 2 \equiv 3 \mod 7\),

and the correct response is 3.

Example Question #1 : Mathematical Relationships

Add:  \(\displaystyle 100+1.01+0.01+0.00001\)

Possible Answers:

\(\displaystyle 101.11001\)

\(\displaystyle 101.12001\)

\(\displaystyle 101.01001\)

\(\displaystyle 101.02001\)

\(\displaystyle 101.02002\)

Correct answer:

\(\displaystyle 101.02001\)

Explanation:

To solve \(\displaystyle 100+1.01+0.01+0.00001\), make sure the digits are aligned with the correct placeholder.  It is also possible to add term by term.

\(\displaystyle 100+1.01= 101.01\)

\(\displaystyle 101.01+0.01= 101.02\)

\(\displaystyle 101.02+ 0.00001=101.02001\)

The correct answer is: \(\displaystyle 101.02001\)

Example Question #4 : Mathematical Relationships

Evaluate: \(\displaystyle (2+1)^3-(3*4)-7+3+(24\div 6)\).

Possible Answers:

\(\displaystyle 12\)

\(\displaystyle 15\)

\(\displaystyle 17\)

\(\displaystyle 14\)

Correct answer:

\(\displaystyle 15\)

Explanation:

Step 1: Recall PEMDAS...

Parentheses, Exponents, Multiplication, Division, Addition, Subtraction.

Step 2: Perform the evaluation in separate pieces...

\(\displaystyle (2+1)^3=3^3=27\)

\(\displaystyle (3*4)=12\)

\(\displaystyle -7+3=-4\)

\(\displaystyle (24\div 6)=4\)

Step 3: Replace the values and keep the signs..

\(\displaystyle 27-12+4-4\)

Step 4: Evaluate:

\(\displaystyle (27-12)+(4-4)=15+0=15\)

 

Example Question #5 : Mathematical Relationships

Find the sum of the numbers:  \(\displaystyle 13+14+88+12+54\)

Possible Answers:

\(\displaystyle 121\)

\(\displaystyle 201\)

\(\displaystyle 181\)

\(\displaystyle 193\)

\(\displaystyle 191\)

Correct answer:

\(\displaystyle 181\)

Explanation:

Add all the ones digits.

\(\displaystyle 3+4+8+2+4 = 21\)

Add the tens digits with the two as the carryover.

\(\displaystyle 1+1+8+1+5+(2) = 18\)

Combine this value with the ones digit of the first number.

The answer is:  \(\displaystyle 181\)

Example Question #1 : Mathematical Relationships

Evaluate:  \(\displaystyle 134+189+879\)

Possible Answers:

\(\displaystyle 1212\)

\(\displaystyle 1202\)

\(\displaystyle 1092\)

\(\displaystyle 1302\)

\(\displaystyle 1112\)

Correct answer:

\(\displaystyle 1202\)

Explanation:

Add the ones digits.

\(\displaystyle 4+9+9 = 22\)

Add the tens digits with the tens digit of the previous number as carryover.

\(\displaystyle 3+8+7+(2) = 20\)

Repeat the process with the hundreds digits.

\(\displaystyle 1+1+8+(2) = 12\)

Combine this number with the ones digits of the previous calculations.

The answer is:  \(\displaystyle 1202\)

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