What are the possible rational zeros for \[f(x) = 4{x^3} - 9{x^2} + 6x - 1\] and how do you find them?
Answer
604.8k+ views
Hint: To solve this question, we first need to find one of the possible rational zeros using the trial-and-error method. Next, we need to divide the original polymer with the factor we obtained using the previously obtained zero. The quotient will be a quadratic equation. We would have to factorize that quadratic equation, obtain all factors of the original polynomial, and then finally find the zeros using the obtained factors.
Complete step-by-step answer:
The Given Polynomial is \[f(x) = 4{x^3} - 9{x^2} + 6x - 1\] .
We need to find out its rational zeros. For the first zero, we need to use the trial-and-error approach.
By trial-and-error approach, we get \[x = 1\] for \[f(x) = 0\] . Thus, \[(x - 1)\] is a factor of \[f(x)\] .
Now, for the rest of the zeroes, we first need to obtain a quadratic expression along with the above factor by dividing \[f(x)\] with \[(x - 1)\] .
On performing the division, we obtain the following expression.
\[f(x) = (x - 1)(4{x^2} - 5x + 1)\] .
For obtaining the remaining zeros, we need to factorize the quadratic part of \[f(x)\] , i.e., \[4{x^2} - 5x + 1\] .
This can be done by splitting \[5x\] into \[x\] and \[4x\] , so that pairing and factorization can be performed.
Thus, we have
\[
f(x) = 4{x^3} - 9{x^2} + 6x - 1 \\
f(x) = (x - 1)(4{x^2} - 4x - x + 1) \\
\Rightarrow f(x) = (x - 1)\left( {4x(x - 1) - 1(x - 1)} \right) \\
\Rightarrow f(x) = (x - 1)\left( {(x - 1)(4x - 1)} \right) \\
\Rightarrow f(x) = (x - 1)(x - 1)(4x - 1) \\
\Rightarrow x = 1,1,\dfrac{1}{4} \;
\]
We obtain \[x = 1,1,\dfrac{1}{4}\] if \[f(x) = 0\] . At these values of \[x\] , the value of \[f(x)\] will be zero. Hence, these values are the rational zeros of \[f(x) = 4{x^3} - 9{x^2} + 6x - 1\] .
So, the correct answer is “ \[x = 1,1,\dfrac{1}{4}\] if \[f(x) = 0\] ”.
Note: In some questions like this, two or more zeros of a polynomial can have the exact same value. However, they are counted as different zeroes. This is because the factors are being repeated in the factored expression of the polynomial.
Complete step-by-step answer:
The Given Polynomial is \[f(x) = 4{x^3} - 9{x^2} + 6x - 1\] .
We need to find out its rational zeros. For the first zero, we need to use the trial-and-error approach.
By trial-and-error approach, we get \[x = 1\] for \[f(x) = 0\] . Thus, \[(x - 1)\] is a factor of \[f(x)\] .
Now, for the rest of the zeroes, we first need to obtain a quadratic expression along with the above factor by dividing \[f(x)\] with \[(x - 1)\] .
On performing the division, we obtain the following expression.
\[f(x) = (x - 1)(4{x^2} - 5x + 1)\] .
For obtaining the remaining zeros, we need to factorize the quadratic part of \[f(x)\] , i.e., \[4{x^2} - 5x + 1\] .
This can be done by splitting \[5x\] into \[x\] and \[4x\] , so that pairing and factorization can be performed.
Thus, we have
\[
f(x) = 4{x^3} - 9{x^2} + 6x - 1 \\
f(x) = (x - 1)(4{x^2} - 4x - x + 1) \\
\Rightarrow f(x) = (x - 1)\left( {4x(x - 1) - 1(x - 1)} \right) \\
\Rightarrow f(x) = (x - 1)\left( {(x - 1)(4x - 1)} \right) \\
\Rightarrow f(x) = (x - 1)(x - 1)(4x - 1) \\
\Rightarrow x = 1,1,\dfrac{1}{4} \;
\]
We obtain \[x = 1,1,\dfrac{1}{4}\] if \[f(x) = 0\] . At these values of \[x\] , the value of \[f(x)\] will be zero. Hence, these values are the rational zeros of \[f(x) = 4{x^3} - 9{x^2} + 6x - 1\] .
So, the correct answer is “ \[x = 1,1,\dfrac{1}{4}\] if \[f(x) = 0\] ”.
Note: In some questions like this, two or more zeros of a polynomial can have the exact same value. However, they are counted as different zeroes. This is because the factors are being repeated in the factored expression of the polynomial.
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