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Hello, can you help me find the solutions to this problem?

Hello, can you help me find the solutions to this problem?-example-1
User Ilbose
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1 Answer

5 votes

Given,

The expression is,


\begin{gathered} x^3=216 \\ x^3-216=0 \end{gathered}

The rational theorem tells that if the polynomial has the rational 0 then it must be a fraction p/q, where p is a factor of constant term and q is the factor of leading coefficient.

The constant term 216 with factors:


1,2,3,4,6,8,9,12,18,24,27,36,54,72,108\text{ }and\text{ }216.

The leading coefficient is 1, with a single factor of 1.


\begin{gathered} (p)/(q)=\frac{factor\text{ of 216}}{factor\text{ of 1}}=\pm(1)/(1),\operatorname{\pm}(2)/(1),\operatorname{\pm}(3)/(1),\operatorname{\pm}(4)/(1),\operatorname{\pm}(6)/(1),\operatorname{\pm}(8)/(1),\operatorname{\pm}(9)/(1),\operatorname{\pm}(12)/(1), \\ \operatorname{\pm}(18)/(1),\operatorname{\pm}(24)/(1),\operatorname{\pm}(27)/(1),\operatorname{\pm}(36)/(1),\operatorname{\pm}(54)/(1),\operatorname{\pm}(72)/(1),\operatorname{\pm}(108)/(1),\operatorname{\pm}(216)/(1) \end{gathered}

Substitute the possible roots one by one into the polynomial to find the actual roots. Start first with the whole numbers.

p(6)=0 so x=6 is a root of a polynomial p(x).

Using factor theorem to find the remaining roots,


\begin{gathered} (x^3-216)/(x-6)=x^2+6x+36 \\ By\text{ formula method,} \\ x=(-6\pm√(36-144))/(2) \\ x=(-6\pm√(108))/(2) \\ x=(-6\pm6√(-3))/(2) \\ x=-3\pm3√(3i) \end{gathered}

Hence, the roots are 6, -3-3sqrt(3)i, and -3+3sqrt(3)i. So, option A is correct.

User Sontek
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