Find the equation of the tangent to the curve y= 4x-tanx at the point where x=pi/4. I tried finding the first derivative and then plugging in values but even my slope is wrong.

Question

anonymous · Answer

you need the first derivative for the slope, not the second

anonymous · Answer

sorry i meant first derivative.

anonymous · Answer

did you get$$y'=4-\sec^2(x)$$?

anonymous · Answer

yes. then i turned it into y'= 4- cosx/sinx and plugged in pi/4

anonymous · Answer

that is your mistake

anonymous · Answer

$$\sec^2(x)=\frac{1}{\cos^2(x)}$$

anonymous · Answer

you were thinking of cotangent , not cosecant

anonymous · Answer

now it should work out, right?

anonymous · Answer

OMG silly error. aha yeah , thanks!

anonymous · Answer

yw