SOLUTION: If z1 = 2cis115° and z2 = 3cis65° , write z1z2 in its RECTANGULAR FORM: a + bi.

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Question 1117277: If z1 = 2cis115° and z2 = 3cis65° , write z1z2 in its RECTANGULAR FORM: a + bi.
Answer by ikleyn(53751) About Me  (Show Source):
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If z1 = 2cis115° and z2 = 3cis65° , write z1z2 in its RECTANGULAR FORM: a + bi.
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z1*z2 = 2*3*cis(115° + 65°) = 6*cis(180°) = 6*(cos(180°) + i*sin*180°)) = 6*(-1 + i*0) = -6.


I first multiplied in trigonometric/polar form, and then transformed to rectangular form  a+bi = -6    (a = -6, b = 0).