SOLUTION: Please help me with this calculus problem involving derivatives of inverse functions. Thank you in advance for your time! <a rel=nofollow HREF="https://ibb.co/L0fMQpv"><img src

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Question 1203750: Please help me with this calculus problem involving derivatives of inverse functions. Thank you in advance for your time!
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Answer by math_helper(2461) About Me  (Show Source):
You can put this solution on YOUR website!

One approach is to find g(x), the inverse of f(x):
f(x) = +sqrt%28x%5E2+%2B+8x%29+, +x%3E=0+
To avoid confusion, I'll use y=f(x), solve for y, and after that, we can write g(x):
f(x) = ++y+=+sqrt%28x%5E2+%2B+8x%29+
Square both sides
+y%5E2+=+%28x%5E2+%2B+8x%29++
Add 16 to both sides, this completes the square on RHS
+y%5E2+%2B+16+=+x%5E2+%2B+8x+%2B+16+
Factor RHS
+y%5E2+%2B+16+=+%28x%2B4%29%5E2+
Take square root of both sides
+sqrt%28y%5E2%2B16%29+=+x+%2B+4+
Subtract 4 from both sides, and re-write with x on LHS:
+x+=+%28sqrt%28y%5E2%2B16%29%29+-+4+

Now we can write +g%28x%29+=+-4+%2B+sqrt%28x%5E2%2B16%29+ , and g(x) also has domain x%3E=0

g'(x) = +%281%2F2%29%28x%5E2%2B16%29%5E%28-1%2F2%29+=++1%2F%282%2Asqrt%28x%5E2%2B16%29%29+

Just plug in x=3 to g(x) and g'(x) to get the desired values ( I got g(3)=1, g'(3)=1/10)