# Math Help - Stationary point...

1. ## Stationary point...

Find the coordinates of the stationary point of the curve $y=e^xcosx$ for 0 is less than or equal to x and x is less than or equal to $/pi$ . Leave your answer in exact form.

2. Originally Posted by Punch
Find the coordinates of the stationary point of the curve $y=e^xcosx$ for 0 is less than or equal to x and x is less than or equal to x . Leave your answer in exact form.
First get dy/dx (use the product rule). Can you do that? Please show all your work and say where you're stuck.

3. $
dy/dx=-e^xsinx
$

am stucked at the part solving for x

4. Originally Posted by Punch
$
dy/dx=-e^xsinx
$

[snip]
Wrong. Have you been taught the product rule? If not, then attempting this question is currently a futile exercise for you. If you have, then I suggest you go to your class notes or textbook and review it.

5. $\frac{dy}{dx} = e^xcosx-e^xsinx$
$= e^x[cosx-sinx]$

now, $e^x[cosx-sinx]=0$ stucked =="

6. Originally Posted by Punch
$\frac{dy}{dx} = e^xcosx-e^xsinx$
$= e^x[cosx-sinx]$
Correct.

Now solve $\frac{dy}{dx} = 0 \Rightarrow \cos x - \sin x = 0 \Rightarrow 1 = \tan x$ over the given domain.

Then find the y-coordinate corresponding to the solutions for x found above.

If you need more help, please show all your work and say where you get stuck.

7. i dont understand the part where u "threw" e^x away... wont u lose a solution? other than this everything else is fine thx

8. Originally Posted by Punch
i dont understand the part where u "threw" e^x away... wont u lose a solution? other than this everything else is fine thx
Do you know what the graph of y = e^x looks like? Can e^x ever equal zero?