求X值 23^x-4=16^x

1）两边取对数,xlg23-lg4=xlg16,则x=lg4/(lg23-lg16)
2）设数为x,则x-1/x=16/15,即15x²-16x-15=0, (5x+3)(3x-5)=0
则x=-3/5或x=5/3
3) (x^3+27)/(x+3) = (x+3)(x²-3x+9)/(x+3) = x²-3x+9
4) sin(x-π/2) =1/2
-sin(π/2-x)=1/2
cosx=-1/2
x=4π/3或2π/3