HSC2014
Member
- Joined
- Jul 30, 2012
- Messages
- 399
- Gender
- Male
- HSC
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Question: Find the square roots of -21 + 20i
My solution:
root (-21 +20 i ) = root [ (2)^2 + (5i)^2 + 2 (2) (5i) ]
= +- (2 + 5i)
Is this acceptable? My concerns involve the shortness of the solution. I expressed -21 + 20i as a perfect square (it is pretty clear to me) and so I am able to obtain the roots very quickly - but I don't know about markers. I don't like the method where i say x^2 - y^2 = -21, and 2xy = 20... etc. I know that is necessary sometimes but not for this question.
My solution:
root (-21 +20 i ) = root [ (2)^2 + (5i)^2 + 2 (2) (5i) ]
= +- (2 + 5i)
Is this acceptable? My concerns involve the shortness of the solution. I expressed -21 + 20i as a perfect square (it is pretty clear to me) and so I am able to obtain the roots very quickly - but I don't know about markers. I don't like the method where i say x^2 - y^2 = -21, and 2xy = 20... etc. I know that is necessary sometimes but not for this question.
Good to know... I don't want my pen to waste ink.