The equation of a polynomial is .
- (i)
Factorise the polynomial .
- (ii)
Determine the nature of the roots of the equation .
- (iii)
Solve the equation .
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Worked solution
4(i)
1. Find a linear factor of the polynomial using the Factor Theorem.
Let .
Try :
.
Since , is a factor.
2. Divide the polynomial by the linear factor to find the quadratic factor.
Using long division or comparing coefficients:
Comparing coefficients:
Comparing constant terms:
Comparing coefficients:
So, .
3. Factorise the quadratic factor completely.
Therefore, .
4(ii)
1. Use the factorised form of $\text{f}(x)$ from part (i) to set up the equation
From part (i), .
For , we have:
2. Identify the real root from the linear factor
This gives one real root.
3. Analyse the quadratic factor using the discriminant
For the quadratic factor , we check the discriminant :
Since , the quadratic equation has no real roots.
4. State the final conclusion about the nature of the roots
Therefore, the equation has exactly one real root.
The equation has exactly one real root.
4(iii)
1. Rewrite the given equation to reveal the polynomial structure from part (i)
2. Substitute $x = 3^y$ and use the roots of $f(x) = 0$ from earlier parts
Let . The equation becomes , which is .
From part (i), .
So the roots are and .
Thus, or .
3. Solve for $y$ using logarithms
For :
For :
or (to 3 s.f.)
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