Trig Differentiation (1 Viewer)

[iPhone4]

Hi guys, I just couldn't get the answer on some practice multiple choice my teacher gave me.

Find the gradient of the normal to the curve y=tanx at the point where x=pi/6.

I kept getting -3/4. The four possible answers are:

a) -1/3
b) 1/(sqrt3)
c) 3
d) -(sqrt3)

 

[Drongoski]

-3/4 should be right. How did you work that out(just whacked into the calculator?)?

 

[iPhone4]

I did:
d/dx tanx = sec^2 x

So the normal is just -cos^2 x
- (cosx)^2
x=30 degrees,

- (sqrt3/2)^2
=-3/4

 

[Drongoski]

Perfect. Just the way to do it.

 

[Nws m8]

Lol at your username