11/23/09
Test 4 Section 6 - #12 (page 597)
Factor x^{2} - y^{2} = 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.
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how do i know here to not subtract the equation (x+y=11) from (x^2-y^2=77)?
ReplyDeleteExperience, mostly. Or you try it and you see that it gets you nowhere, so you try something else.
ReplyDelete