Homework Help: Calculus

Posted by Allison on Saturday, March 12, 2011 at 9:19pm.

a)
Find a Cartesian equation relating and corresponding to the parametric equations: x=2sin(3t), y=9cos(3t).
Write your answer in the form P(x,y)=0, where P(x,y) is a polynomial in x and y, such that the coefficient of y^2 is 4.

b)Find the equation of the tangent line to the curve at the point corresponding to t=pi/9

Calculus - MathMate, Saturday, March 12, 2011 at 9:38pm
(a)
x=2sin(3t)....(1)
y=9cos(3t)....(2)
square each equation
x²=4sin²(3t)...(1a)
y²=81cos²(3t)...(2a)
divide by coefficient of RHS and add:
(x²/4+y²/81)=sin²(3t)+cos²(3t)=1
(x²/4+y²/81)-1=0
Multiply by 4*81 to have common denominator of 1
P(x,y)=81x²+4y²-324=0

b.
To find tangent, calculate dy/dx=y'(x,y) using implicit differentiation.
dy/dx at t0=pi/9:
evaluate m=y'(2sin(3t0), 9cos(3t0))

Equation of tangent line:
L : (y-9cos(3t0))=m(x-2sin(3t0))

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