Question #976bb

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Answer 1 · 2017-03-14T07:40:49

# (i) : 4cis120^@=-2+i2sqrt3; (ii) : 9cis(3pi/2)=-9i.#

Recall that, #rcis theta=r(cos theta +i sin theta).#

# (i) 4cis 120^@=4(cos 120^@ + i sin 120^@)#

#=4{cos (90^@+30^@)+isin(90^@+30^@)}#

#=4{-sin30^@+icos30^@}#

#=4{-1/2+isqrt3/2}#

#:. 4cis 120^@=-2+i2sqrt3.#

Similarly, #(ii) : 9cis(3pi/2)=-9i.#

Enjoy Maths.!