Question

已知函数f（x）=2+log以3为底数x的对数,x∈[1/81,81],求函数g（x）=[f（x）]^2-f（x^2）的

Answer 1

g（x）=[f（x）]^2-f（x^2）=[2+log3(x)]^2-2-2log3(x)=[log3(x)]^2+2log3(x)+2

用换元法 令 log3(x)=t

y=t^2+2t+2

(-4