Answer:
2
Step-by-step explanation:
Hello,
[tex]x=(fof^{-1})(x)=f(f^{-1}(x))=\sqrt{2f^{-1}(x)}+5\\<=>\sqrt{2f^{-1}(x)} =x-5\\<=>2f^{-1}(x)=(x-5)^2\\<=>f^{-1}(x)=\dfrac{(x-5)^2}{2}[/tex]
now let's replace x by 7 it comes
[tex]f^{-1}(7)=\dfrac{(7-5)^2}{2}=\dfrac{2^2}{2}=2[/tex]
hope this helps
