问题补充:
(x+y)的平方+10(x+y)+25因式分解已知x的平方+kx-12=(x+2)(x+n),则k=
答案:
解(x+y)²+10(x+y)+25
=(x+y)²+2×5×(x+y)+5²——将x+y看成整体
=[(x+y)+5]²
=(x+y+5)²
(x+2)(x+n)
=x²+nx+2x+2n
=x²+(n+2)x+2n
=x²+kx-12
∴2n=-12,n+2=k
∴n=-6,k=-4
4a²+12a+9
=(2a)²+2×2a×3+3²
=(2a+3)²
∵a>0∴2a+3>:0∴边长为2a+3