90/(x-90)=(2x-50)/(x+50)

(2x-50)(x-90)=90(x+50)
2x^2-230x+4500=90x+4500
2x^2-230x-90x+4500-4500=0
2x^2-320x=0
x^2-160x=0
x(x-160)=0
x1=0x2=160那个……^是什么意思^2 是平方