Date | May 2014 | Marks available | 6 | Reference code | 14M.1.hl.TZ2.4 |
Level | HL only | Paper | 1 | Time zone | TZ2 |
Command term | Find | Question number | 4 | Adapted from | N/A |
Question
The roots of a quadratic equation \(2{x^2} + 4x - 1 = 0\) are \(\alpha \) and \(\beta \).
Without solving the equation,
(a) find the value of \({\alpha ^2} + {\beta ^2}\);
(b) find a quadratic equation with roots \({\alpha ^2}\) and \({\beta ^2}\).
Markscheme
(a) using the formulae for the sum and product of roots:
\(\alpha + \beta = - 2\) A1
\(\alpha \beta = - \frac{1}{2}\) A1
\({\alpha ^2} + {\beta ^2} = {(\alpha + \beta )^2} - 2\alpha \beta \) M1
\( = {( - 2)^2} - 2\left( { - \frac{1}{2}} \right)\)
\( = 5\) A1
Note: Award M0 for attempt to solve quadratic equation.
[4 marks]
(b) \((x - {\alpha ^2})(x - {\beta ^2}) = {x^2} - ({\alpha ^2} + {\beta ^2})x + {\alpha ^2}{\beta ^2}\) M1
\({x^2} - 5x + {\left( { - \frac{1}{2}} \right)^2} = 0\) A1
\({x^2} - 5x + \frac{1}{4} = 0\)
Note: Final answer must be an equation. Accept alternative correct forms.
[2 marks]
Total [6 marks]