# Derivative of trigonometric

• October 8th 2008, 09:27 PM
JimDavid
Derivative of trigonometric
Quote:

Find the points on the curve y= tan x, -pi/2< x < pi/2, where the tangent is parallel to the line y= 2x.
How do you do this? I'm really confused (Headbang)
• October 8th 2008, 09:28 PM
Jhevon
Quote:

Originally Posted by JimDavid
How do you do this? I'm really confused (Headbang)

you want all the points where the derivative has a value of 2. so find the derivative, set it equal to 2 and solve for x
• October 8th 2008, 09:38 PM
JimDavid
Quote:

Originally Posted by Jhevon
you want all the points where the derivative has a value of 2. so find the derivative, set it equal to 2 and solve for x

I turned tan x into sec^2 x, so it's 2=sec^2? How do you suppose to solve for it?
• October 8th 2008, 09:47 PM
Jhevon
Quote:

Originally Posted by JimDavid
I turned tan x into sec^2 x, so it's 2=sec^2? How do you suppose to solve for it?

yes, $\frac d{dx} \tan x = \sec^2 x$

now recall that $\sec x = \frac 1{\cos x}$