X^2-4X-12=0
（x-6)(x+2)=0
x=6或x=-2
X+2X^2-15=0
(x+5)(x-3)=0
x=-5或x=3
24X-3X^2=0
8x-x^2=0
x(8-x)=0
x=0或x=8
已知（X+Y）^2-2X-2Y+1=0,求2X^2+4XY+2Y^2的值
(x+y)^2-2x-2y+1=0
(x+y)^2-2(x+y)+1=0
(x+y-1)^2=0
x+y=1
2x^2+4xy+2y^2
=2(x^2+2xy+y^2)
=2(x+y)^2
=2*1^2
=2
已知a,b,c为三角形三边,试判断a^2-2ab+b^2-c^2大于0还是小于0还是等于0
a^2-2ab+b^2-c^2
=(a-b)^2-c^2
=(a-b-c)(a-b+c)(根据两边之和大于第三边,a-b-c