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# C4 differentiation help! watch

1. Hey!

The question is:

Find the equation of the normal to the curve with parametric equations x=e^t,
y= e^t + e^-t, at the point P, where t= 0.

Here's what i get,
dx/dt = e^t. dy/dt = e^t - e^-t

when you dy/dx it and substitute t=0, the dy/dx= 0 since dy/dx = (e^t - e^-t)/e^t.... Right?

So, how do i get the equation of normal when the gradient of tangent is zero?
2. (Original post by ACatCalledMeow)
Hey!

The question is:

Find the equation of the normal to the curve with parametric equations x=e^t,
y= e^t + e^-t, at the point P, where t= 0.

Here's what i get,
dx/dt = e^t. dy/dt = e^t - e^-t

when you dy/dx it and substitute t=0, the dy/dx= 0 since dy/dx = (e^t - e^-t)/e^t.... Right?

So, how do i get the equation of normal when the gradient of tangent is zero?
If the gradient of the tangent is zero, then it is parallel to the x axis. So the normal must therefore be parallel to the y axis. So you just need to find an x value.
3. (Original post by Freerider101)
If the gradient of the tangent is zero, then it is parallel to the x axis. So the normal must therefore be parallel to the y axis. So you just need to find an x value.
Why didn't i think of that?

THANKS! ahhhhh feel so stupid now. Thanks again!

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