Question

若(x+y-5)^2+lx-y+3l=0

x^2-y^2=？

Answer 1

因为 (x+y-5)^2 >=0, lx-y+3l >=0, (x+y-5)^2+lx-y+3l=0
所以 (x+y-5)^2 =0, lx-y+3l =0
所以 x+y = 5, x-y = -3
所以 x^2-y^2 = (x+y)*(x-y) = -15

Answer 2

由上式可知：x+y=5
x-y=-3;
x=1;y=4; x^2-y^2=-15;

Answer 3

wo shu xue bu hao
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