已知X十y=5⃣️Xy=2⃣️求(x-y)^2.x^4+y^4的值
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已知X十y=5⃣️Xy=2⃣️求(x-y)^2.x^4+y^4的值
已知X十y=5⃣️Xy=2⃣️求(x-y)^2.x^4+y^4的值
已知X十y=5⃣️Xy=2⃣️求(x-y)^2.x^4+y^4的值
读不懂题
(x-y)的平方=x的平方-2xy+y的平方=(x+y)的平方-4xy=25-8=17
(x—y)^2=x^2-2xy+y^2=(x+y)^2+4xy=5^2+4*2=33
x^4+y^4=(x^2+y^2)^2—2(xy)^2=【(x+y)^2—2xy】^2—2(xy)^2=21^2—8
(X-Y)^2=(X+Y)^2-4XY=17
x^2+y^2=(X+Y)^2-2XY
x^4+y^4=( x^2+y^2)^2-2 x^2y^2=((X+Y)^2-2XY)^2-2 x^2y^2=433