Question

prove geometrically cos(A+B)=cosA.cosB-sinA.sinB and hence show that cos (90+x)= - sinx​

Answer 1

cos(a+b)=AC−BC=AC−FD

                    =cos(a)cos(b)−sin(a)sin(b)

sin(a+b)=BF+FE=CA+FE

                  =sin(a)cos(b)+

Answer 2

Answer:

cos(90+x)=cos90.cosx-sin90.sinx)

cos90=0,cos0.cosx=0,sin90=1

0-1.sinx=-sinx

hence proved that cos(90+x)=-sinx

Step-by-step explanation: