i need help reducing this using cosabcosacosbsinasinb Reduci

i need help reducing this using cos(a-b)=cosa*cosb+sina*sinb

Reducing this using cos(a-b)=cosa*cosb+sina*sinb 17.1415 times Cos(pi t/12) - 5.0432 times Sin(pi t/12)

17.1415cos(pi*t/12) - 5.0432sin(pi*t/12)

Lets divide and multiply num and den by = sqrt( 17.415^2 +5.0432^2) = 17.87

17.87 {17.1415/17.87cos(pi*t/12) - 5.0432/17.87sin(pi*t/12) }

Now 17.1415/17.87 = cosx

and 5.0432/17.87 = sinx ----> x = 0.286 radians

So, 17.87(cosx*cos(pi*t/12) - sinx*sin(pi*t/12) )

= 17.87{ cos(x +pi*t/12)

= 17.87{cos(pi*t/12 +0.286) }