x^2+[1/4(56-4x)]^2=200
x^2+(14-x)^2=200
x^2+196-28x+x^2=200
2x^2-28x=4
x^2-14x=2
(x-7)^2=2+49
(x-7)^2=51
x-7=±√51
所以x1=7+√51 x2=7-√51