已知x+y=8,1/2x²+xy+1/2y²的值是____
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已知x+y=8,1/2x²+xy+1/2y²的值是____
已知x+y=8,1/2x²+xy+1/2y²的值是____
已知x+y=8,1/2x²+xy+1/2y²的值是____
(x^2+2xy+y^2)/2
=(x+y)^2/2
=8^2/2
=32
1/2x²+xy+1/2y² =1/2 (x²+2xy+y²) =1/2(x+y)² = 1/2 * 8*8=32
因为x+y=8,所以(x+y)²=64=x²+2xy+y²
所以1/2x²+xy+1/2y²=32.