Homework Help: Differntiate the function

1. Jun 2, 2010

ghostbuster25

ok just want a check of my work before i send it :)

differntiate the function;
f(x)=$$\frac{x(20-x)}{36}$$

so,
f'(x)=$$\frac{(20x-x^2)}{36}$$

f'(x)=$$\frac{(20-2x)}{36}$$

f'(x)=$$\frac{(10-2x)}{18}$$

Then....use the composite rule and your answer above to differntiate the function
g(x)=ex(20-x)/36

g'(x)=f'(x)*ef(x)

so,
g'(x)=$$\frac{10-2x)}{18}$$*g(x)=ex(20-x)/36

is this correct?

is this correct

2. Jun 2, 2010

Staff: Mentor

Re: differentiation

Above - This is not f'(x). All you have done is expand the numerator on the right. This should be f(x) = ...
Above - Now you have taken the derivative
Above - now you have an error. 20 - 2x != 2(10 - 2x).
Where f(x) = (1/36)(x(20 - x)). The derivative below is incorrect. To fix it, replace f'(x) and f(x) where they appear.