Question if-and

2.4 Equivalent Expressions - Simplifying rational expressions
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If x squared equals, a, plus b and y squared equals, a, plus c, which of the following is equal to open parenthesis, x squared, minus y squared, close parenthesis, squared ?

A.

a, squared, minus 2 a, c, plus c squared

B.

b squared, minus 2 b c, plus c squared

C.

4, a, squared, minus 4 a, b c, plus c squared

D.

4 a, squared, minus 2 a, b c, plus b squared c squared

If and , which of the following is equal to ?

Hard-difficulty · SAT Math · Equivalent Expressions — Simplifying rational expressions. Read the question above, select your answer, and check the full explanation below to understand exactly why the correct choice works.

Answer explanation

Choice B is correct. It’s given that x squared equals, a, plus b and y squared equals, a, plus c. Using the distributive property, the expression open parenthesis, x squared, minus y squared, close parenthesis, squared can be rewritten as open parenthesis, x squared, close parenthesis, squared, minus 2 x squared, times y squared, plus, open parenthesis, y squared, close parenthesis, squared. Substituting a, plus b and a, plus c for x squared and y squared, respectively, in this expression yields open parenthesis, a, plus b, close parenthesis, squared, minus, 2 times, open parenthesis, open parenthesis, a, plus b, close parenthesis, times, open parenthesis, a, plus c, close parenthesis, close parenthesis, plus, open parenthesis, a, plus c, close parenthesis, squared. Expanding this expression yields open parenthesis, a, squared, plus 2 a, b, plus b squared, close parenthesis, minus, open parenthesis, 2 a, squared, plus 2 b c, plus 2 a, c, plus 2 a, b, close parenthesis, plus, open parenthesis, a, squared, plus 2 a, c, plus c squared, close parenthesis. Combining like terms, this expression can be rewritten as b squared, minus 2 b c, plus c squared.

Choices A, C, and D are incorrect and may result from an error in using the distributive property, substituting, or combining like terms.