Question

Find exact value of cos(7pi)

Answer 1

-1

Answer 2

http://www.wolframalpha.com/input/?i=cos%287pi%29 use the website

Answer 3

Remember cosx starts and ends with value 1: cos(0) = 1, cos(2pi)=1.
Its period is 2pi.
Max values at beginning and end, so min value in the middle: cos(pi) = -1.

Because the period is 2pi, adding 2pi doesn't make a difference: you end up at the same height.

So: cos(pi) = cos(3pi) = cos(5pi) = cos(7pi) = -1.

Answer 4

-1

Answer 5

approx =.9272

Answer 6

-1