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# Core 3 , reciprocal of differentiation questions watch

1. Find dx/dy of
a) 3+4sin5x

For this I've found dy/dx is 20cox5x however I can't get the dx/dy!!

b) y=3e^sin2x ---> asks me to show dx/dy=sec2x/2y

So far I've worked out 1/6cos2x * e^sin2x! Where do I go on from these??????

Help much appreciated, please explain how to get 2y..... thankyouuuuu
2. (Original post by plower)
Find dx/dy of
a) 3+4sin5x

For this I've found dy/dx is 20cox5x however I can't get the dx/dy!!

b) y=3e^sin2x ---> asks me to show dx/dy=sec2x/2y

So far I've worked out 1/6cos2x * e^sin2x! Where do I go on from these??????

Help much appreciated, please explain how to get 2y..... thankyouuuuu
RDKGames
3. (Original post by plower)
Find dx/dy of
a) 3+4sin5x

For this I've found dy/dx is 20cox5x however I can't get the dx/dy!!
Take reciprocals of both sides

b) y=3e^sin2x ---> asks me to show dx/dy=sec2x/2y

So far I've worked out 1/6cos2x * e^sin2x! Where do I go on from these??????

Help much appreciated, please explain how to get 2y..... thankyouuuuu
Check your differential, it should be a 6, not 1/6.

For dx/dy just take the reciprocal of both sides, then cosine being on the denominator is the same as secant being on the numerator. Then for the rest of the denominator, take out a certain number as a factor so you'd get that number multiplied by the expression for y.

(Original post by Maths is Life)
RDKGames
Basic C3
4. (Original post by RDKGames)
Take reciprocals of both sides
Ok I got 1/20 * sec5x ??

(Original post by RDKGames)

Check your differential, it should be a 6, not 1/6.

For dx/dy just take the reciprocal of both sides, then cosine being on the denominator is the same as secant being on the numerator. Then for the rest of the denominator, take out a certain number as a factor so you'd get that number multiplied by the expression for y.
Oh yah I meant dy/dx I got 6cos2x*e^sin2x and for dx/dy = 1/6cos2x*e^sin2x . To simplify, I tried to do what you said so then I worked out 1/cos2x * 1/6e^sin2x which is sec2x/6e^sin2x ....... no 2y . Do you mean like say for example I factorised it like 2(3e^sin2x) then say y=3e^sin2x so then it's 2y?
5. (Original post by plower)
Ok I got 1/20 * sec5x ??

Oh yah I meant dy/dx I got 6cos2x*e^sin2x and for dx/dy = 1/6cos2x*e^sin2x . To simplify, I tried to do what you said so then I worked out 1/cos2x * 1/6e^sin2x which is sec2x/6e^sin2x ....... no 2y . Do you mean like say for example I factorised it like 2(3e^sin2x) then say y=3e^sin2x so then it's 2y?
Both correct.
6. (Original post by RDKGames)
Both correct.
Oooo Thankyou guys so much!!!

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