Diverted Vieta

Algebra Level 4

If m 3 12 m n 2 = 40 m^3 - 12mn^2 = 40 and 4 n 3 3 m 2 n = 10 4n^3 - 3m^2n = 10 , find m 2 + 4 n 2 m^2 + 4n^2 . Round off your answers to four decimal places.


The answer is 12.5992.

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1 solution

Rajen Kapur
May 1, 2017

( m + 2 i n ) 3 = m 3 + 6 i m 2 n 12 m n 2 8 i n 3 = 40 20 i , w h e r e i = 1 (m+2in)^3 =m^3+6im^2n-12mn^2-8in^3=40-20i,where\ \ i=\sqrt{-1} Multiplying both sides with their complex conjugates, we get ( m 2 + 4 n 2 ) 3 = 4 0 2 + 2 0 2 = 2000 (m^2+4n^2)^3=40^2+20^2=2000 . Answer is 200 0 1 3 12.5992 2000^\frac{1}{3}\approx12.5992 .

Nicely done!

James Wilson - 3 years, 3 months ago

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