抛物线y^2=4x焦点为(1,0)设过焦点的直线方程为：y=k(x-1)则代入y^2=4x得：k^2(x-1)^2=4xk^2x^2-(2k^2+4)x+k^2=0x1+x2=(2k^2+4)/k^2,x1x2=1(x1-x2)^2=(x1+x2)^2-4x1x2=16(1+k^2)/k^4所以,弦长=√（1+k^2)(x1-x2)^2=4...