For a complex number z=a+bi it can be represented as z=r(cosθ+isinθ) where r=√a2+b2 and θ=tan−1(ba)
2+i14+9i=√22+12(cos(tan−1(12))+isin(tan−1(12)))√142+92(cos(tan−1(914))+isin(tan−1(914)))≈√5(cos(0.46)+isin(0.46))√277(cos(0.57)+isin(0.57))
Given z1=r1(cosθ1+isinθ1) and z2=r2(cosθ2+isinθ2), z1z2=r1r2(cos(θ1−θ2)+isin(θ1−θ2))
z1z2=√5√277(cos(0.46−0.57)+isin(0.46−0.57))=√1385277(cos(−0.11)+isin(−0.11))≈√1385277(0.99−0.11i)≈0.134−0.015i
Proof:
2+i14+9i⋅14−9i14−9i=28−4i+9142+92=37−4i277≈0.134−0.014i