若x2-3x+a=（x-5)(x-b),则a·b=x^2-3x+a=x^2-(5+b)x+5b5+b=3b=-25b=a=-10a*b=20若4a2+kab+9b2是完全平方式,则常数k=k^2-4*4*9=0k^2=114k=12 or k=-12若a-b=13,a2-b2=39,则a2+b2+2ab=a^2-b^2=(a+b)(a-b)=39a+b=3a^2+b...