Monday, August 4, 2014

What is x if 64x^3+1331=0?

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


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


a^3 = 64x^3


a =
4x


b^3 = 11^3


b =
11


64x^3+1331 = (4x+11)(16x^2 - 44x +
121)


If 64x^3+1331 = 0, then (4x+11)(16x^2 - 44x + 121) =
0


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


4x+11 = 0


We'll
subtract 11 both sides:


4x =
-11


x1 = -11/4


16x^2 - 44x +
121 = 0


We'll apply the quadratic
formula:


x2 = [44 +
sqrt(1936-7744)]/2


x2 =
(44+44isqrt3)/32


We'll factorize by 44 the
numerator:


x2 =
44(1+isqrt3)/32


x2 =
11(1+isqrt3)/8


x3 =
11(1-isqrt3)/8


The roots of the equation are:
{-11/4 , 11(1-isqrt3)/8, 11(1+isqrt3)/8 }.

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