Come si dimostra #cos (pi / 2 + theta) = -sin (theta) #?

#cos (a+b)=cosacosb-sinasinb#

lasciare #a=pi/2 & b= theta#

#=>cos(pi/2+theta)=cos(pi/2)cos(theta)-sin(pi/2)sin(theta)#

#=>cos(pi/2+theta)=(0)costheta-(1)sintheta#

#=>cos(pi/2+theta)=0-sintheta#

#=>cos(pi/2+theta)=-sintheta#