Can any one help with October 21, 2006 PSAT questions in Math?

Test Preparation SAT Preparation
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<p>Please look at:</p>

<p>page #14 Question no 20. Both x=y and x=-y are good. Why is it x=y must be true?</p>

<p>page # 28, Question no 37. I am lost in this question. Please helppppppppppppp.</p>