11/23/09

Test 4 Section 6 - #12 (page 597)

Factor x2 - y2 = 77 into (x+y)(x-y) = 77. Since we know x+y=11, that means x-y=7. Solve those equations to get x=9 and y=2.

2 comments:

  1. how do i know here to not subtract the equation (x+y=11) from (x^2-y^2=77)?

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  2. Experience, mostly. Or you try it and you see that it gets you nowhere, so you try something else.

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