Derivative of an inverse for Calc 1

  • Thread starter aero13
  • Start date
  • #1
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Homework Statement


Find (f−1)'(a).
f(x) = 5x^3 + 3x^2 + 5^x + 4, a = 4

Homework Equations


I'm not entirely sure but I assume I have to use d/dx(f-1) = 1/f '(f-1(x))


The Attempt at a Solution


So far I switched y and x. Found dx/dy to be 15y^2 + 6y + 5. Then I switched dx/dy to dy/dx so the answer became 1/15^2 + 6y +5 and I plugged in 4 to get 1/269. But the answer is wrong
 

Answers and Replies

  • #2
761
13
No, do not plug in 4 solve the equation being equal to 4.
 
  • #3
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Ok so I set 1/15y^2 + 6y + 5 equal to 4. Ended up with 1 = 4(15y^2 + 6y + 5) so 1 = 60y^2 + 24y +20. Do I factor it from here?
 

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