(2x+1)^4=140x^3
(4x^2+1+4x)^2=140x^3
(16x^4+1+16x^2+8x^2+8x+32x^3)=140x^3
16x^4+1+16x^2+8x^2+8x+32x^3=140x^3
16x^4-108x^3+24x^2+8x+1=0
[4x^2-13.5x]^2-(12.58x+0.3138)^2+0.9=0
x解得0.108