Question

Find the points on the given curve where the tangent line is horizontal or vertical.
r = 3cos(theta)

Answer 1

Use

y=rsin(theta)
x=rcos(theta)

Take dy/dx .. take it from here?

Answer 2

yup got it thanks

Answer 3

YEAAH!

Answer 4

well i actually have to do it but haha your not completely right atm lemme see

Answer 5

actually don't you use the polar curve formula of dy/dx = rcos(theta) + sin(theta) (dr/d(theta)) / -rsin(theta)+cos(theta) (dr/d(theta))? then just set top = 0 or the bottom = 0?

Answer 6

So when your dx=0 you have a vertical tangent line.
Actually for this equations there are alot of points where it should be vertical

and the horizontal points aren't quite as easy because you have to solve something like

3(cos^2(theta)-sin^2(theta))=0

Answer 7

yep thats exactly what you do, the formula you typed is just the product rule for derivatives

Answer 8

actually not quite

Answer 9

alrighty. easy enough. thanks =)

Answer 10

yep :)