# Math Help - differentiating trig ratios

1. ## differentiating trig ratios

find the equation of the tangent to the curve y=cosA + 3sinA at the point where A= pi/2
so i took A=pi/2 to get y= 2sqrt2 and m=sqrt2, with the resulting equation being y=sqrt2(A+2-(pi/2))
apparently that is so wrong, and the answer is y+A=3+(pi/2)
i need help here

2. Originally Posted by furor celtica
find the equation of the tangent to the curve y=cosA + 3sinA at the point where A= pi/2
so i took A=pi/2 to get y= 2sqrt2 and m=sqrt2, with the resulting equation being y=sqrt2(A+2-(pi/2))
apparently that is so wrong, and the answer is y+A=3+(pi/2)
i need help here
Derivative is $-\sin A+3\cos A$. Plug in $\pi/2$ to get $m=-1$. Go from there.

3. ha ha good point i had plugged in pi/4
thanks