3分之2的x次冪加9分之4的x次冪=1
(2/3)^x+(4/9)^x=1
(2/3)^2x+(2/3)^x+1/4=1+1/4
((2/3)^x+1/2)^2=5/4
(2/3)^x+1/2=√5/2或(2/3)^x+1/2=-√5/2 （不合題意舍去）
(2/3)^x+1/2=√5/2
(2/3)^x=√5-1/2
lg(2/3)^x=lg(√5-1/2)
x=lg(√5-1/2)/lg(2/3)
x=1.17