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Express the following numbers in the form x + iy: 7(cos(-5π6)+isin(-5π6))

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Question

Express the following numbers in the form x + iy:

`7(cos(-(5pi)/6) + "i" sin (- (5pi)/6))`

Sum
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Solution

`cos(-(5pi)/6) = cos  (5pi)/6 = cos(pi - pi/6)`

= `-cos  pi/6`

= `-sqrt(3)/2`

and `sin(- (5pi)/6)`

= `-sin  (5pi)/6`

= `-sin(pi - pi/6)`

= `-sin  pi/6`

= `-1/2`

∴ `7[cos(-(5pi)/6) + "i" sin(-(5pi)/6)]`

= `7[ - sqrt(3)/2 + "i"(-1/2)]`

= `-(7sqrt(3))/2 - (7"i")/2`, which is of the form x + iy.

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Chapter 1: Complex Numbers - Exercise 1.3 [Page 15]

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