Given #f(t) = -3/(2t+1)# and #g(t) = 7/(t^2)#, what is #g(f^-1(t))#?

1 Answer
May 21, 2017

#g(f^(- 1)(t)) = frac(28 t^(2))((t + 3)^(2))#; #t ne - 3#

Explanation:

First, let's evaluate the inverse of #f(t)#, i.e. #f^(- 1)(t)#:

#Rightarrow f(t) = - frac(3)(2 t + 1)#

Let's replace #f(t)# with #s#:

#Rightarrow s = - frac(3)(2 t + 1)#

Interchanging variables:

#Rightarrow t = - frac(3)(2 s + 1)#

We need to solve this equation for #s#:

#Rightarrow - frac(t)(3) = frac(1)(2 s + 1)#

#Rightarrow (- frac(t)(3))^(- 1) = (frac(1)(2 s + 1))^(- 1)#

#Rightarrow - frac(3)(t) = 2 s + 1#

#Rightarrow 2 s = - frac(3)(t) - 1#

#Rightarrow 2 s = - frac(3)(t) - frac(t)(t)#

#Rightarrow 2 s = - frac(3 + t)(t)#

#Rightarrow s = - frac(3 + t)(2 t)#

Let's replace #s# with #f^(- 1)(t)#:

#therefore f^(- 1)(t) = - frac(t + 3)(2 t)#

Now, let's evaluate #g(f^(- 1)(t))#

#Rightarrow g(f^(- 1)(t)) = g(- frac(t + 3)(2 t))#

#Rightarrow g(f^(- 1)(t)) = frac(7)((- frac(t + 3)(2 t))^(2))#

#Rightarrow g(f^(- 1)(t)) = frac(7)(frac((t + 3)^(2))(4 t^(2)))#

#Rightarrow g(f^(- 1)(t)) = 7 cdot frac(4 t^(2))((t + 3)^(2))#

#therefore g(f^(- 1)(t)) = frac(28 t^(2))((t + 3)^(2))#; #t ne - 3#