Wednesday, February 29, 2012

Let F(x)=f(x^9) and G(x)=(f(x))^9 and suppose that a^8=6, f(a)=2, f′(a)=12, f′(a^9)=4 find F'(a) and G'(a)

We begin by stating the given information: 


`F (x) = f(x^9)` ... Eq. 1.1


`G(x) = (f(x))^9` ... Eq. 1.2


Additionally we are given :


`a^8 = 6`  ... Eq. 2.1


`f(a) = 2` ... Eq. 2.2 


`f'(a) = 12` ... Eq. 2.3


`f'(a^9) = 4` ... Eq. 2.4


We are required to find: 


`F'(a) = ?`


And 


We have to use to above equation to solve what is required. Let's begin by solving F'(a): 


If `F(x) = f(x^9)`


` `


 Then using the chain rule :


`F'(x) = f'(x^9) * 9x^8`


Therefore applying ourselves, by substituting 'a' for 'x': 


`F' (a) = f'(a^9) * 9a^8`


We can now substitute Eq. 2.4 and Eq. 2.1


`F'(a) = 4 * 9(6) = 216` 


We have solved the first part, now let's solve the last part: 


If `G(x) = (f(x))^9`


Then using the chain rule: 


`G'(x) = 9[f(x)}^8 * f'(x)`


Now we can apply ourselves by substituting 'a' for 'x':


`G'(a) = 9 [f(a)]^8 * f'(a)`  


Now substitute eq. 2.2 and eq. 2.3 in the above equation: 


`G'(a) = 9* (2)^8 * 12 = 27648`


SUMMARY: 


F'(a) = 216


G'(a) = 27648

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