IGCSE/GCSE/O & A Level/IB/University Student Forum

Qualification => Subject Doubts => GCE AS & A2 Level => Math => Topic started by: T.Q on January 17, 2010, 08:36:05 am

Title: need help in C3
Post by: T.Q on January 17, 2010, 08:36:05 am

Given that x = 4 sin (2y + 6), find dy/dx in terms of x.

my answer to the Q was  dy/dx= 1/8cos(2y+6)     
but i didnt know how to write it in term of x can someone help me plz

Title: Re: need help in C3
Post by: XFlufferzX on January 17, 2010, 04:56:46 pm

x = 4 sin (2y + 6)

Sin (2y +6) = x/4

where x = opp.
         4 = hyp.
To find adjacent uuse Pythagoras theorem

adj = sqrt 16 - x^2

Cos ( 2y +6) = adj / hyp
                  = (sqrt. 16 - x^2)/4

dy/dx = 1/8cos(2y+6)
Simplify

1/8 . 1/cos(2y+6)

1/8 . 1/ sqrt. 16 - x^2 / 4

= 1/2 sqrt 16 - x^2

eh If yuh couldnt understand wat I did let me know
check da attached paper

Title: Re: need help in C3
Post by: T.Q on January 17, 2010, 05:23:55 pm

thank you:)

Title: Re: need help in C3
Post by: astarmathsandphysics on January 17, 2010, 07:31:10 pm

See this for implicit differentiation

http://www.astarmathsandphysics.com/a_level_maths_notes/C3/a_level_maths_notes_c3_implicit_differentiation.html

I am just about to finish the C3 notes. Start C4 tomorrow

Title: Re: need help in C3
Post by: T.Q on January 17, 2010, 07:36:52 pm

Quote from: astarmathsandphysics on January 17, 2010, 07:31:10 pm

See this for implicit differentiation

http://www.astarmathsandphysics.com/a_level_maths_notes/C3/a_level_maths_notes_c3_implicit_differentiation.html

I am just about to finish the C3 notes. Start C4 tomorrow

thank you so much ,
very helpful