（7x-1)^2=4x^2
(7x-1)²=4x²
（7x-1)²-4x²=0
(7x-1-2x)(7x-1+2x)=0
(5x-1)(9x-1)=0
5x-1=0 X1=1/5
9x-1=0 X2=1/9
∴X1=1/5
X2=1/9
用因式分解法解(7x-1)^2=4x^2
（7x-1)^2=4x^2
(7x-1)²=4x²
（7x-1)²-4x²=0
(7x-1-2x)(7x-1+2x)=0
(5x-1)(9x-1)=0
5x-1=0 X1=1/5
9x-1=0 X2=1/9
∴X1=1/5
X2=1/9