4(x+3)^2=25(x-2)^2
(2x+6)^2=(5x-10)^2
(5x-10)^2-(2x+6)^2=0
(5x-10+2x+6)(5x-10-2x-6)=0
(7x-4)(3x-16)=0
x=4/7,或x=16/3(2x+6)^2=(5x-10)^2这部是怎么得来的？