(x-2)^2=(2x+5)^2x^2-4x+4=4x^2+20x+253x^2+24x+21=0x^2+8x=7=0 因式分解（x+1)（x+7)=0x=-1 或x=-7
(x-2)^2 - (2x+5)^2 =0用平方差公式分解：[(x-2) + (2x+5)] [(x-2) - (2x+5)] = 0化简 (x+1) (x+7) = 0所以x=-7 或 x=-1
