- #1
[ScPpL]Shree
- 3
- 0
Homework Statement
If y=f((x2+9)0.5) and f'(5)=-2, find dy/dx when x=4
Homework Equations
chain rule: dy/dx=(dy/du)(du/dx)
The Attempt at a Solution
In my opinion giving f'(5)=-2 is unnecessary as:
y=f(u)=u, u=(x2+9)0.5
dy/dx= (dy/du)(du/dx)
(dy/du)= 1
(du/dx)= x/((x2+9))0.5
dy/dx = (1)(x/((x2+9))0.5)
= x/((x2+9))0.5
dy/dx(4) = 4/(16+9)0.5
= 4/(25)0.5
= 4/5
the answer is -8/5
I would appreciate help very much.