crazy math question

Test Preparation SAT Preparation
1

<p>hey guys im stumped on this problem</p>

<p>If (x+y)(x^2-y^2)=0, which of the following must be true?</p>

<p>a) x=y
b) x=-y
c) x^2=y^2
d)x^2=-y^2
e)x^3=y^3</p>

<p>My answer was A. actually, i thought that either a,b, or c could be right. So i just went with A.
the correct answer is c.
. I know that c, makes sense, but what makes a and b wrong.</p>

<p>thanks</p>

2

<p>Factors, (x+y)^2(x-y) = 0.</p>

<p>Either x+y = 0, or x-y = 0, that is, x=±y. Thus, x^2 = y^2 for all solutions x,y.</p>

3

<p>The question asks which of answer choice MUST be true. The correct answer is x=y or x=-y. Therefore, either answer choice A or B can be correct but not must be correct.
Only answer choice C is true all the time.</p>