Answer
$10[\cos40^{\circ}+i \sin40^{\circ}]$
Work Step by Step
$if\\$
$z_{1}=r_{1}(\cos\theta_1+i\sin\theta_1)\\$
$ and \\$
$z_{2}=r_{2}(\cos\theta_2+i\sin\theta_2)\\$
$then\\$
$z_1z_2 = r_1r_2[\cos(\theta_1+\theta_2)+i \sin(\theta_1+\theta_2)]$
$given\ problem\\$
$5(cos 15° + i sin 15°) \cdot2(cos 25° + i sin 25°)\\$
$here\ r_1=5, r_2=2, \theta_1=15, \theta_2=25\\$
$5*2[\cos(15^{\circ}+25^{\circ})+i \sin(15^{\circ}+25^{\circ})\\$
$10[\cos40^{\circ}+i \sin40^{\circ}]$
