3,4题帮下忙,
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3,4题帮下忙,3,4题帮下忙, 3,4题帮下忙,3.(1)(-2x+5)^2-(-2x-5)^2=4x^2-20x+25-(4x^2+20x+25)=-20x(2)(x-y)(x^2-y^
3,4题帮下忙,
3,4题帮下忙,
3,4题帮下忙,
3.(1)(-2x+5)^2-(-2x-5)^2
=4x^2-20x+25-(4x^2+20x+25)
=-20x
(2)(x-y)(x^2-y^2)(x+y)
=(x^2-y^2)^2
=x^4-2(xy)^2+y^4
4.将两式相加得:
2(x^2+y^2)=10
x^2+y^2=5
将x^2+y^2=5代入其中一式
解得:xy=1
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3,4,
3,4,
3,4,