Answer
$12[cos50^{\circ}+isin50^{\circ}]$
Work Step by Step
$if\\ $
$z_1=r_1(cosθ_1+isinθ_1)\\$
$and\\$
$z_2=r_2(cosθ_2+isinθ_2)\\$
$then\\$
$z_1z_2=r_1r_2[cos(θ_1+θ_2)+isin(θ_1+θ_2)]$
$given\ problem\\$
$3(cos 20° +i sin 20°) 4(cos 30° + i sin 30°)\\$
$here\ r1=3,r2=4,θ1=20,θ2=30\\$
$=3∗4[cos(20^{\circ}+30^{\circ})+isin(20^{\circ}+30^{\circ})\\$
$=12[cos50^{\circ}+isin50^{\circ}]$
