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A2 Maths help

I have two questions which I'm really stuck on and i was wondering if you could show me how to do them

Given x= cos(3y) find a) dx/dy in terms of y b)find dy/dx in terms of y ( i get thats one over part a but i got -sin(3y) which i don't think can be right)

c) hence find the equation of the normal to the curve x+cos(3y) at the point where y= π/6

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Last question is find the coordinates of the stationary points of the curve y= √2x+5 - x . the 2x+5 is all square rooted and the -x isn't. thanks in advance I really appreciate it!
Original post by joeheat
I have two questions which I'm really stuck on and i was wondering if you could show me how to do them

Given x= cos(3y) find
a) dx/dy in terms of y
b)find dy/dx in terms of y

( i get thats one over part a but i got -sin(3y) which i don't think can be right)


What did you get for (a) is that the -Sin(3y) if so - apply the chain rule
Original post by joeheat

Last question is find the coordinates of the stationary points of the curve y= √2x+5 - x . the 2x+5 is all square rooted and the -x


y=2x+5x=(2x+5)12xy=\sqrt{2x+5} - x = (2x+5)^{\frac{1}{2}} -x

I assume that you have learnt the chain rule - can you apply it to this

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