According to the Rational Root Theorem, which could be a factor of the polynomial f(x) = 6x4 – 21x3 – 4x2 + 24x – 35?

A2x – 7
B2x + 7
C3x – 7
D3x + 7

Verified Answer :

the answer is the first option, A) 2x-7

Answer with explanation:

The given Polynomial function is

\(f(x)= 6x^4 - 21 x^3 - 4 x^2 + 24 x - 35\\\\6(x^4-\frac{21}{6}\times x^3-\frac{4}{6}\times x^2+4 x-\frac{35}{6})\)

By Rational root Theorem ,factors of the above expression can be

\(\text{Factors of 35,factors of 6,and factors of }\frac{35}{6}=\pm 1,\pm 5,\pm 7, \pm 35,\pm 2,\pm 3, \pm 6\)

\(,\pm \frac{1}{2},\pm\frac{1}{3},\pm \frac{1}{6},\pm\frac{5}{2},\pm\frac{5}{3},\pm\frac{5}{6},\pm\frac{7}{2},\pm\frac{7}{3},\pm\frac{7}{6},\pm\frac{35}{2},\pm\frac{35}{3},\pm\frac{35}{6}\)

That is , by observing at the options, the factors of the given expression could be

\(x=\pm \frac{7}{2}\\\\ \text{and}, x=\pm \frac{7}{3}\)

Substituting these four  Values one by one  in the Polynomial function

  \(f(\frac{7}{2})=6 \times (\frac{7}{2})^4 -21 \times (\frac{7}{2})^3 -4 \times (\frac{7}{2})^2 +24 \times (\frac{7}{2})-35\\\\ f(\frac{7}{2})=900.375 -900.375 - 49+84-35\\\\f(\frac{7}{2})=0\)

As,we have to find single factor,you will find that,

\(f(\frac{-7}{2}) eq 0 \text{and} f(\frac{\pm7}{3}) eq 0.\)

So, \(x=\frac{7}{2}\\\\ 2x-7\)

is the factor of the polynomial.

Option A: 2 x -7