Posted by **Daniel** on Friday, October 14, 2011 at 10:10pm.

Find an equation of the tangent line to the curve at

y = cosx - sinx (pi, -1)

I found y'= -sinx - cosx

and used the equation of the tangent

y = mx +b

I input the values and get -1 - [(-sinx - cosx) * pi] = b

the answer says it is y = x - 1 - pi

I have no idea how the answer got that.

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