z=a+bi=r(cosθ+isinθ)
r=√a2+b2, θ=tan−1(ba)
r1(cos(θ1)+isin(θ2))+r2(cos(θ2)+isin(θ2))=r1cos(θ1)+r2cos(θ2)+i(r1sin(θ1)+r2sin(θ2))
r1=√82±22)=√68
r2=√72±32=√58
θ1=tan−1(−28)≈345.96∘, IV quadrant
θ2=tan−1(−37)≈336.8∘, IV quadrant
z1+z2=√68cos(345.96)+√58cos(336.8)+i(√68sin345.96+√58sin336.8)
⇒8+7+i(−2−3)
⇒15−5i