Calculus
posted by StevE
Find the derivatives of the following
18. y=〖cos〗^4 x^4
ANSWER: tanx2
19. y= sinx/(1+ 〖cos〗^2 x)
ANSWER: 3sinx
20. y=sinx(sinx+cosx)
ANSWER: sinx
Can you check my answers?

Steve
wow  remember the chain rule
if u = cos(x^4) then we have
y = u^4
y' = 4u^3 u'
y' = 4 cos^3(x^4) * (sin(x^4)(4x^3)
= 16x^3 sin(x^4) cos^3(x^4)
y = sinx/(1+cos^2(x))
y' = [(cosx)(1+cos^2(x))  (sinx)(2cosx)(sinx)]/(1+cos^2(x))^2
y = sinx(sinx+cosx)
y' = cosx(sinx+cosx) + sinx(cosxsinx)
I think you have some serious reviewing to do. I'd love to see the stepbystep work you did to get your answers. 
Damon
4 cos^3 x^4 sin x^4 (4 x^3)
=  16 x^3 cos^3 x^4 sin x^4
how that is tan x2 whatever that is I can not imagine 
StevE
ohhh.. I think I know what I did wrong.. I did not even realize that I was doing something completely different
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