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need c3 help

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T.Q:
A curve C has equation

y=3sin2x+4cos2x,

The point A(0, 4) lies on C.
 
(a) Find an equation of the normal to the curve C at A

when i defferintiate i got this dy/dx= 6cos2x - 8sin2x

my problem was when i subsituted the  x=0 i had the wrong value of the gradient

in the MS m=6

show your working

astarmathsandphysics:

--- Quote from: T.Q on December 20, 2009, 04:58:25 pm ---A curve C has equation

y=3sin2x+4cos2x,

The point A(0, 4) lies on C.
 
(a) Find an equation of the normal to the curve C at A


show your working

--- End quote ---

dy/dx=6cos2x-8sin2x so gradient m=6cos(2*0)-8sin(2*0)=6 and m for normal is -1/6
y-y1=m(x-x1)
y-4=-1/6(x-0) so y=-x/6+4

T.Q:

--- Quote from: astarmathsandphysics on December 20, 2009, 05:12:25 pm ---dy/dx=6cos2x-8sin2x so gradient m=6cos(2*0)-8sin(2*0)=6 and m for normal is -1/6
y-y1=m(x-x1)
y-4=-1/6(x-0) so y=-x/6+4

--- End quote ---
thanx now i got it

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