f(x)=x^a
图像过p(3,27开4次),
3^a=27^(1/4)=[(3^3)]^(1/4)=3^(3/4)
所以a=3/4〉0
g(x)=x^b
图像过q(-8,-2),
(-8)^b=-2
(-2)^3b=(-2)^1
3b=1
b=1/3
f(x)