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January 26, 2015

January 26, 2015

Posted by **Jackie** on Sunday, April 17, 2011 at 12:56pm.

5(cos Pi/3 + i sin Pi/3)times 2 (cos Pi/4 + i sin Pi/4) and leave the answer in trigonometric notation.

- trig -
**MathMate**, Sunday, April 17, 2011 at 7:08pmUsing the following result:

(cosα+isinα)(cosβ+isinβ)

=cosαcosβ-sinαsin&beta + i(sinαcosβ+cosαsinβ)

=cos(α+β) + i sin(α+β)

So

5(cos Pi/3 + i sin Pi/3)times 2 (cos Pi/4 + i sin Pi/4)

is simply

5*2 (cos(π/3+π4)+i sin(π/3+π/4))

=10(cos(7π/12)+i sin(7π/12))

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