Answer:
a) C = A cos φ , S = A sin φ
Explanation:
a) The two equations given are equivalent ,
we know the formula of
Cos (a + b) = cos a cos b - sin a sin b
let say
a = ωt and b = φ
x(t) = A (cos ωt cosφ- sin ωt sin φ )
the second equation is
x(t) = C cos ωt + S sin ωt
they both are equivalent
C cos ωt + S sin ωt = A cos φ cosωt - a sin φ sin ωt
The coefficients of the equation should be equal
C = A cos φ
S = A sin φ