(90-x)/(180-x)=3/7

问题描述:

(90-x)/(180-x)=3/7

90-x 3
----- = -----
180-x 7
630-7x=540-3x
630=540+4x
x=22.5

十字相乘
7*(90-x)=3*(180-x)
x=22.5

(90-x)/(180-x)=3/7
7(90-x)=3(180-x)
630-7x=540-3x
4x=90
x=45/2