ISEE Upper Level Quantitative : How to add exponential variables

Study concepts, example questions & explanations for ISEE Upper Level Quantitative

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Example Questions

Example Question #211 : Algebraic Concepts

Simplify:

\(\displaystyle 5x^{2} y ^{2}+7 + 6x^{2}y^{2} + 11 xy\)

Possible Answers:

The expression cannot be simplified further

\(\displaystyle 11x^{2}y^{2}+ 11 xy +7\)

\(\displaystyle 22x^{3}y^{3}+7\)

\(\displaystyle 29x^{3}y^{3}\)

\(\displaystyle 30x^{2}y^{2}+ 11 xy +7\)

Correct answer:

\(\displaystyle 11x^{2}y^{2}+ 11 xy +7\)

Explanation:

Group and combine like terms \(\displaystyle 5x^{2} y ^{2},6x^{2}y^{2}\):

\(\displaystyle 5x^{2} y ^{2}+7 + 6x^{2}y^{2} + 11 xy\)

\(\displaystyle = 5x^{2} y ^{2}+ 6x^{2}y^{2}+ 11 xy +7\)

\(\displaystyle =\left ( 5+ 6 \right )x^{2}y^{2}+ 11 xy +7\)

\(\displaystyle =11x^{2}y^{2}+ 11 xy +7\)

Example Question #51 : Variables

\(\displaystyle x > 0, y < 0\)

Which is the greater quantity?

(a) \(\displaystyle (x + y)^{2}\)

(b) \(\displaystyle x^{2}+ y^{2}\)

Possible Answers:

It is impossible to tell from the information given.

(b) is greater.

(a) is greater.

(a) and (b) are equal.

Correct answer:

(b) is greater.

Explanation:

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

Since \(\displaystyle x\) and \(\displaystyle y\) have different signs,

\(\displaystyle xy< 0\), and, subsequently,

\(\displaystyle 2xy < 0\)

Therefore, 

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

This makes (b) the greater quantity.

Example Question #1 : How To Add Exponential Variables

Assume that \(\displaystyle x\) and \(\displaystyle y\) are not both zero. Which is the greater quantity?

(a) \(\displaystyle \frac{(x+y)^{2} + (x - y)^{2}}{x^{2}+y^{2}}\)

(b) \(\displaystyle 4xy\)

Possible Answers:

(a) and (b) are equal.

It is impossible to tell from the information given.

(a) is greater.

(b) is greater.

Correct answer:

It is impossible to tell from the information given.

Explanation:

Simplify the expression in (a):

\(\displaystyle \frac{(x+y)^{2} + (x - y)^{2}}{x^{2}+y^{2}}\)

\(\displaystyle =\frac{(x^{2}+2xy + y^{2})+ (x^{2}-2xy + y^{2})}{x^{2}+y^{2}}\)

\(\displaystyle =\frac{ x^{2}+x^{2} +2xy -2xy+ y^{2}+ y^{2}}{x^{2}+y^{2}}\)

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

Therefore, whether (a) or (b) is greater depends on the values of \(\displaystyle x\) and \(\displaystyle y\), neither of which are known. 

Example Question #1 : Variables And Exponents

\(\displaystyle x > 0\)

Which is the greater quantity?

(a) \(\displaystyle x^{2} + 3x\)

(b) \(\displaystyle 4x\)

Possible Answers:

It is impossible to tell from the information given

(b) is greater

(a) and (b) are equal

(a) is greater

Correct answer:

It is impossible to tell from the information given

Explanation:

We give at least one positive value of \(\displaystyle x\) for which (a) is greater and at least one positive value of \(\displaystyle x\) for which (b) is greater.

Case 1: \(\displaystyle x = 2\)

(a) \(\displaystyle x^{2} + 3x = 2^{2} + 3 \cdot 2 = 4 + 6 = 10\)

(b) \(\displaystyle 4x = 4 \cdot 2 = 8\)

Case 2: \(\displaystyle x = \frac{1}{2}\)

(a) \(\displaystyle x^{2} + 3x = \left ( \frac{1}{2} \right ) ^{2} + 3 \cdot \frac{1}{2} = \frac{1}{4} + \frac{3}{2} = \frac{7}{4}= 1 \frac{3}{4}\)

(b) \(\displaystyle 4x = 4 \cdot \frac{1}{2} = 2\)

Therefore, either (a) or (b) can be greater.

Example Question #1 : Variables And Exponents

Assume all variables to be nonzero. 

Simplify: \(\displaystyle \left (12x^{5}y ^{4}z^{3} \right )^{0} + \left (3x^{5}y ^{4}z^{3} \right )^{0}\)

Possible Answers:

\(\displaystyle 15x^{10}y ^{8}z^{6}\)

None of the answer choices are correct.

\(\displaystyle 36x^{10}y ^{8}z^{6}\)

\(\displaystyle 36x^{5}y ^{4}z^{3}\)

\(\displaystyle 15x^{5}y ^{4}z^{3}\)

Correct answer:

None of the answer choices are correct.

Explanation:

Any nonzero expression raised to the power of 0 is equal to 1. Therefore, 

\(\displaystyle \left (12x^{5}y ^{4}z^{3} \right )^{0} + \left (3x^{5}y ^{4}z^{3} \right )^{0} = 1 + 1 = 2\).

None of the given expressions are correct.

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