McGraw Hill Integrated II, 2012
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McGraw Hill Integrated II, 2012 View details
10. Roots and Zeros
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Exercise 19 Page 77

Factor by applying the sum of cubes.

Roots: x=-1, x= 1± isqrt(3)2
Number and Type of Roots: one real root, two imaginary roots

Practice makes perfect

To solve the given equation, we will apply the sum of cubes. a^3+b^3 ⇔ (a+b)(a^2-ab+b^2) Let's start by factoring the left-hand side.

x^3+1=0
â–¼
Factor left-hand side
x^3+1^3=0

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

(x+1)(x^2-x* 1+1^2)
(x+1)(x^2-x+1^2)
(x+1)(x^2-x+1) =0
We have rewritten the left-hand side as a product of two factors. Now, we will apply the Zero Product Property to solve the equation.

(x+1)(x^2-x+1) =0
lcx+1=0 & (I) x^2-x+1=0 & (II)
lx=-1 x^2-x+1=0

From Equation (I), we found that one root is x=- 1. To find other roots, we will solve Equation (II). Note that this is a quadratic equation. Thus, we will use the Quadratic Formula. ax^2+bx+c=0 ⇕ x=- b±sqrt(b^2-4ac)/2a To do so, we first need to identify a, b, and c. x^2-x+1=0 ⇕ 1x^2+( - 1)x+ 1=0 We see that a= 1, b= - 1, and c= 1. Let's substitute these values into the formula and evaluate the right-hand side. Remember that sqrt(- a)= isqrt(a).

x=- b±sqrt(b^2-4ac)/2a
x=- ( - 1)±sqrt(( - 1)^2-4( 1)( 1))/2( 1)
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Solve for x
x=1±sqrt((- 1)^2-4(1)(1))/2(1)
x=1±sqrt(1-4(1)(1))/2(1)
x=1±sqrt(1-4)/2
x=1±sqrt(- 3)/2
x = 1± isqrt(3)/2

These roots of the quadratic equation are also roots of the given equation. Roots x=- 1, x=1 ± isqrt(3)/2 There are three roots. One of these roots is real and two of them are imaginary.