What is the slope of the line normal to the tangent line of f(x) = xsecx-cos(2x-pi/6) f(x)=xsecxcos(2xπ6) at x= (15pi)/8 x=15π8?

1 Answer
Feb 19, 2018

0.2865...

Explanation:

So first derive the equation, then plug in x into the derivative, then find the negative reciprocal of that slope to get the normal slope.

Use product rule to derive the first part:
d/dx[xsec(x)]= sec(x)+ xtan(x)sec(x)ddx[xsec(x)]=sec(x)+xtan(x)sec(x)
Chain rule to derive second part:
d/dx[-cos(2x-pi/6)]=2sin(2x-pi/6)ddx[cos(2xπ6)]=2sin(2xπ6)
Put these together so the derivative is
f'(x)= sec(x)+ xtan(x)sec(x)+2sin(2x-pi/6)
Plug in x=(15pi)/8 to get the slope of the parallel line as -3.49041.
The slope of the normal (perpendicular) is the negative reciprocal of that slope, which will be 0.2865