Sunday, January 3, 2016

Find all the solutions of the equation 216x^3+2197=0?

To solve the binomial equation, we'll apply the identity
of the sum of cubes:


a^3 + b^3 = (a+b)(a^2 - ab +
b^2)


a^3 =216x^3


a =
6x


b^3 = 13^3


b =
13


216x^3+2197 = (6x+13)(36x^2 - 78x +
169)


If 216x^3+2197 = 0, then (6x+13)(36x^2 - 78x + 169) =
0


If a product is zero, then each factor could be
zero.


6x+13 = 0


We'll
subtract 13 both sides:


6x =
-13


x1 = -13/6


36x^2 - 78x +
169 = 0


We'll apply the quadratic
formula:


x2 = [78 +
sqrt(6084-24336)]/72


x2 =
(78+i*sqrt18252)/72


We'll factorize by 78 the
numerator:


x2 = (78+78i*sqrt
3)/72


x2 = 13(1+isqrt3)/12


x3
= 13(1-isqrt3)/12


The roots of the equation
are: {-13/6 , 13(1+isqrt3)/12, 13(1-isqrt3)/12}.

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