若a^2+b^2=2c^2.若 ,则直线ax+by+c=0 被圆 x^2+y^2=1所截得的弦长为 (

a^x^2=(by+c)^2
x^2+y^2=1
(by+c)^2+a^2y^2-a^2=0
(a^2+b^2)y^2+2bcy+c^2-a^2=0
(y1-y2)^2=2a^2/(a^2+b^2)
b^y^2=(ax+c)^2
b^2x^2+(ax+c)^2-b^2=0
(x1-x2)^2=2b^2/(a^2+b^2)
弦长
=√[(y1-y2)^2+(x1-x2)^2]
=√[2a^2/(a^2+b^2)+2b^2/(a^2+b^2)]
=√[2(a^2+b^2)/(a^2+b^2)]
=√2