# Thread: differentiate arcsin, need to check if I've done right

1. ## differentiate arcsin, need to check if I've done right

I have done another one, which is f(x)= 8arcsin(x^4);

f’(x) = 8 (1/(sqrt(1 – (x^4)^2))*4x^3 =>

f’(x)=32x^3/(sqrt(1 – (x^4)^2))=>

f’(x)=32x^3/(sqrt(1 – (x^8))=>, after that

f’(0.8) = 32*0.512/(sqrt(1 – 0.16777216) =>

f’(0.8) = 16, 384/ (sqrt 0.83222784) = 16, 384/ (0.91226) = 17, 95979

Didn't apply the logs this time (but I wanted so much )
Thanks

2. ## Re: differentiate arcsin, need to check if I've done right

Thanks guys,

Don't bother, I checked and it's correct,

3. ## Re: differentiate arcsin, need to check if I've done right

Don't have to apply log when it is not required. remember we need to apply when we have a function to the power of a function that is [f(x)]^g(x). For example x^y=y^x; [cosx]^y= [siny]^x etc.

4. ## Re: differentiate arcsin, need to check if I've done right

Originally Posted by ibdutt
Don't have to apply log when it is not required. remember we need to apply when we have a function to the power of a function that is [f(x)]^g(x). For example x^y=y^x; [cosx]^y= [siny]^x etc.
ok... now makes sense for me,

thank you

-dokrbb