Question

已知(x+y)²=1 (x-y)²=1 49,求x²+y²与xy的值

Answer 1

已知(x+y)²=1 (x-y)²=1 49,
x²+y²
=[(x+y)²+(x-y)²]÷2
=(1+149)÷2
=75;
与xy的值
=[(x+y)²-(x-y)²]÷4
=(1-149)÷4
=-37;

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Answer 2

知(x+y)²=1 (x-y)²=1 49,求x²+y²与xy的值

x²+y² = [(x+y)²+ (x-y)² ] ÷2
= (1+1 49 ) ÷2
= 75

xy = [(x+y)²- (x-y)² ] ÷4
= (1 - 149) ÷4
= -37