Determining perpendicular tangent line

[Thendi]

Homework Statement

Determine the coordinates of the points on the graph of f(x) = _/'2x+1 where the tangent line is perpendicular to the line 3x+y+4 = 0

_/' -means square root

Homework Equations

f(x) = _/'2x+1
3x+y+4 = 0

The Attempt at a Solution

I made it equal to y
like y= -3x-4...do I have to find the derivative of f(x) = _/'2x+1
Can somebody show me what I am suppose to do next?
or step by step would be fine too.

 

[micromass]

What does the derivative of f(x) tell you about, the tangent line?

 

[HallsofIvy]

Okay, y= -3x- 4 which means it has slope -3. And that tells you than a perpendicular line must have slope 1/3. Where on the curve does the tangent line have slope 1/3?

By the way, just "sqrt(2x+1)" if a far superior notation to "_/'2x+1".

 

[Thendi]

I found the derivative of sqrt(2x+1) which is (2x+1)^1/2

Where on the curve does the tangent line have slope 1/3?

Do you use the chair rule?