1.27: Past-paper question 8

4PM1/1R/June/2025 — Question 8 · 15 marks

f(x)=2x24x+9f(x) = 2x^2 - 4x + 9
The curve C\displaystyle C has equation y=f(x)\displaystyle y = f(x)
The line l\displaystyle l with equation y8x+9=0\displaystyle y - 8x + 9 = 0 is a tangent to C\displaystyle C
The line k\displaystyle k is perpendicular to l\displaystyle l and is also the tangent to C\displaystyle C at the point where x=p\displaystyle x = p
(a) Find the value of p\displaystyle p
(5)
(b) Show that
(i)(α+β)3=α3+β3+3αβ(α+β)(i) (\alpha + \beta)^3 = \alpha^3 + \beta^3 + 3\alpha\beta(\alpha + \beta)
(ii)α4+β4=((α+β)22αβ)22(αβ)2(ii) \alpha^4 + \beta^4 = \left((\alpha + \beta)^2 - 2\alpha\beta\right)^2 - 2(\alpha\beta)^2
(2)
The quadratic equation f(x)=0\displaystyle f(x) = 0 has roots α\displaystyle \alpha and β\displaystyle \beta
Without solving the equation and using your results from part (b)
(c) form a quadratic equation with integer coefficients, that has roots
α3βandβ3α\alpha^3 - \beta \mathrm{and} \beta^3 - \alpha
(8)