How do you prove #cos (pi-x) =- cosx#?
1 Answer
Jan 31, 2016
Use the cosine subtraction formula to expand the term.
Explanation:
Use the cosine subtraction formula:
#cos(alpha-beta)=cos(alpha)cos(beta)+sin(alpha)sin(beta)#
When applied to
#cos(pi-x)=cos(pi)cos(x)+sin(pi)sin(x)#
Simplify.
#cos(pi-x)=(-1)cos(x)+(0)sin(x)#
#cos(pi-x)=-cos(x)#
