1. I assume that there is a typo and your function reads:
2. do you want to find the equation of the tangent line at the graph of your function with the tangent point (1, -1)? If so:
The slope of the tangent has the same value as the gradient of the function in the tangent point.
Calculate the 1st derivation:
EDIT: As angel.white pointed out I've made one of my usual silly mistakes. The following calculations are corrected - by me! Therefore check my calculations!
. Now plug in x = 1. You'll get
That means the tangent has a slope of m = -5.
Now use point-slope-formula of a straight line: