PSAT Math : Algebra

Study concepts, example questions & explanations for PSAT Math

varsity tutors app store varsity tutors android store

Example Questions

Example Question #9 : How To Multiply Complex Numbers

What is the eighth power of \(\displaystyle 1+ i\) ?

Possible Answers:

\(\displaystyle 8 - 8i\)

\(\displaystyle 16\)

\(\displaystyle 8 + 8i\)

The correct response is not given among the other choices.

\(\displaystyle 256i\)

Correct answer:

\(\displaystyle 16\)

Explanation:

First, square \(\displaystyle 1+ i\) using the square of a binomial pattern as follows:

 

\(\displaystyle \left (1+ i \right )^{2}\)

\(\displaystyle = 1^{2}+ 2 \cdot 1 \cdot i + i^{2}\)

\(\displaystyle = 1 +2i -1\)

\(\displaystyle = 2i\)

 

Raising this number to the fourth power yields the correct response:

 

\(\displaystyle \left (1+ i \right )^{8}\)

\(\displaystyle = \left [\left (1+ i \right )^{2} \right ]^{4}\)

\(\displaystyle = (2i)^{4}\)

\(\displaystyle = (2 )^{4} \cdot i^{4}\)

\(\displaystyle =16 \cdot 1 = 16\)

Example Question #10 : How To Multiply Complex Numbers

What is the ninth power of \(\displaystyle -2i\) ?

Possible Answers:

\(\displaystyle 18i\)

\(\displaystyle -18i\)

None of the other responses is correct.

\(\displaystyle 512 i\)

\(\displaystyle -512 i\)

Correct answer:

\(\displaystyle -512 i\)

Explanation:

\(\displaystyle \left ( -2i\right )^{9}\)

\(\displaystyle = \left ( -2 \right )^{9} \cdot i^{9}\)

To raise a negative number to an odd power, take the absolute value of the base to that power and give its opposite:

\(\displaystyle \left ( -2\right )^{9} = - \left ( 2^{9}\right ) = -512\)

To raise \(\displaystyle i\) to a power, divide the power by 4 and raise \(\displaystyle i\) to the remainder. Since 

\(\displaystyle 9 \div 4 = 2 \textup{ R }1\),

\(\displaystyle i^{9} = i^{1}= i\)

Therefore, 

\(\displaystyle \left ( -2i\right )^{9}= \left ( -2 \right )^{9} \cdot i^{9} = -512 i\)

Example Question #11 : Complex Numbers

Simplify:

\(\displaystyle \small \left ( 3 - 2i \right )\left ( 2 + i\right )\)

Possible Answers:

\(\displaystyle \small 6 + 3i\)

\(\displaystyle \small 6 - i\)

\(\displaystyle \small 8 + i\)

\(\displaystyle \small 6 - 3i\)

\(\displaystyle \small 8 - i\)

Correct answer:

\(\displaystyle \small 8 - i\)

Explanation:

Use the FOIL method that states to multiply the Firsts, Outter, Inner, Lasts. Also remember that \(\displaystyle \small i \times i = -1\) :

 

\(\displaystyle \small \left ( 3 - 2i \right )\left ( 2 + i\right )\) 

\(\displaystyle \small = 3 \times 2 + 3 \times i - 2i \times 2 - 2i \times i\)

\(\displaystyle \small = 6 +3i -4i + 2\)

\(\displaystyle \small = 8 - i\)

 

Example Question #1 : Exponential Ratios And Rational Numbers

If \(\displaystyle m\) and \(\displaystyle n\) are positive integers and \(\displaystyle 4^m=64^n\), then what is the value of \(\displaystyle \frac{m}{n}\)?

Possible Answers:

\(\displaystyle \frac{1}{16}\)

\(\displaystyle 3\)

\(\displaystyle 16\)

\(\displaystyle \frac{1}{3}\)

\(\displaystyle \frac{5}{3}\)

Correct answer:

\(\displaystyle 3\)

Explanation:

43 = 64

Alternatively written, this is 4(4)(4) = 64 or 43 = 641.

Thus, m = 3 and n = 1.

m/n = 3/1 = 3.

Example Question #2 : Exponential Ratios And Rational Numbers

Write the following logarithm in expanded form:

 

\(\displaystyle \log x^{2}y\)

Possible Answers:

\(\displaystyle 2\log x+\log y\)

\(\displaystyle \log x^{2}+\log y\)

\(\displaystyle 2\left ( \log xy \right )\)

\(\displaystyle 2\log x-\log y\)

\(\displaystyle \log x+\log y\)

Correct answer:

\(\displaystyle 2\log x+\log y\)

Explanation:

\(\displaystyle \log x^{2}y=\log x^{2}+\log y=2\log x+\log y\)

Example Question #6 : How To Find An Exponent From A Rational Number

Com_exp_1

Which of the following lists the above quantities from least to greatest?

Possible Answers:

I, III, II, IV

II, III, I, IV

IV, III, II, I

I, IV, III, II

I, IV, II, III

Correct answer:

I, III, II, IV

Explanation:

Com_exp_2

Com_exp_3

Example Question #1 : Exponents And Rational Numbers

Solve for \(\displaystyle x\).

2^{x}= 64\(\displaystyle 2^{x}= 64\)

Possible Answers:

\(\displaystyle x=64^{2}\)

\(\displaystyle x=-6\)

\(\displaystyle x=64\)

\(\displaystyle x=5\)

\(\displaystyle x=6\)

Correct answer:

\(\displaystyle x=6\)

Explanation:

Since 2^{x}= 2^{6}\(\displaystyle 2^{x}= 2^{6}\)

Hence \(\displaystyle x=6\)

Example Question #91 : Exponents

Simplify:

 

\(\displaystyle \sqrt[3]{x^{10}y^{8}z^{9}}\)

Possible Answers:

\(\displaystyle \sqrt[3]{xy^{2}}\)

\(\displaystyle x^{3}y^{2}z^{3}\sqrt[3]{xy^{2}}\)

\(\displaystyle x^{3}y^{3}z^{3}\)

\(\displaystyle x^{3}y^{2}z^{3}\)

\(\displaystyle x^{3}y^{2}z^{3}^{\sqrt[3]{xyz}}\)

Correct answer:

\(\displaystyle x^{3}y^{2}z^{3}\sqrt[3]{xy^{2}}\)

Explanation:

\(\displaystyle \sqrt[3]{x^{9}xy^{6}y^{2}z^{9}}=x^{3}y^{2}z^{3}\sqrt[3]{xy^{2}}\)

Example Question #2 : Exponential Ratios And Rational Numbers

Solve for \(\displaystyle x\):

\(\displaystyle \sqrt{x} -1= 4\)

Possible Answers:

\(\displaystyle 9\)

\(\displaystyle 5\)

\(\displaystyle 25\)

\(\displaystyle 5\)

\(\displaystyle 36\)

Correct answer:

\(\displaystyle 25\)

Explanation:

From the equation one can see that

\(\displaystyle \sqrt{x} = 5\)

Hence \(\displaystyle x\) must be equal to 25.

Example Question #2 : How To Find An Exponent From A Rational Number

Evaluate:

\(\displaystyle \log 0.1=\)

Possible Answers:

\(\displaystyle -2\)

\(\displaystyle -1\)

\(\displaystyle 10\)

\(\displaystyle 1\)

\(\displaystyle \frac{1}{10}\)

Correct answer:

\(\displaystyle -1\)

Explanation:

\(\displaystyle 0.1= 10^{-1}\)

\(\displaystyle \log 0.1=-1\)

Learning Tools by Varsity Tutors