why (-a) raise to power b is  equal to a raise to power b

(-a) raise to power b =

(a raise to power b) when b is even

-(a raise to the power b) when b is odd

Example:

(-2) raise to power 3 = (-2)*(-2)*(-2)=-8=-(2 power 3)

(-2) raise to power 4 = (-2)*(-2)*(-2)*(-2)=16=(2 power 4)

Hope you get it!!!