解
(a+b+1)(a+b-1)=63吧
[(a+b)+1][(a+b)-1]=63
(a+b)²-1=63
∴(a+b)²=64
∴a+b=±8
x²+kx+1/4
=(x-1/2)²
=x²-x+1/4
∴k=-1
7x²-28
=7(x²-4)
=7(x-2)(x+2)
(m+n)²-(m-n)²
=[(m+n)-(m-n)][(m+n)+(m-n)]
=(2n)(2m)
=4mn
x+y=2,xy=7
∴x²y+xy²
=xy(x+y)
=7×2
=14