| 4(a) | \includegraphics[max width=\textwidth, alt={}]{6280d53b-3c1c-4dc9-a96b-2c58f2a7bf51-22_199_391_282_420} | | Give B1 if: just one obvious flaw in sketch, or if part of curve for negative \(r\) given, e.g. |
| 4(b) | \(\frac { 1 } { 2 } \int _ { \pi / 3 } ^ { 5 \pi / 3 } \left( \frac { 1 } { 2 } - \cos \theta \right) ^ { 2 } d \theta\) \(\begin{gathered} = \frac { 1 } { 2 } \int _ { \pi / 3 } ^ { 5 \pi / 3 } \left( \frac { 1 } { 4 } - \cos \theta + \cos ^ { 2 } \theta \right) d \theta |
| = \frac { 1 } { 2 } \int _ { \pi / 3 } ^ { 5 \pi / 3 } \left( \frac { 3 } { 4 } - \cos \theta + \frac { 1 } { 2 } \cos 2 \theta \right) d \theta |
| = \frac { 1 } { 2 } \left[ \frac { 3 } { 4 } \theta - \sin \theta + \frac { 1 } { 2 } \sin 2 \theta \right] _ { \pi / 3 } ^ { 5 \pi / 3 } |
| = \frac { 1 } { 2 } \pi + \frac { 3 } { 8 } \sqrt { 3 } \end{gathered}\) | | | Correct expression for area | | Multiply out and use \(\cos 2 \theta\) | | Correct integrand (ignore leading 1/2) | | Correct indefinite integral (ignore leading 1/2) | | Final answer, this or clear exact equivalent only |
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| 5(a) | 2 | A1 | |
| 5(b) | | Roots are \(\alpha ( 1 + 1 / 2 ) , \beta ( 1 + 1 / 2 ) , \chi \left( 1 + \frac { 1 } { 2 } \right)\) | | Hence put \(y = 3 x / 2\) \(x = 2 y / 3\) | | \(3 ( 2 y / 3 ) ^ { 3 } + 2 ( 2 y / 3 ) ^ { 2 } - 7 ( 2 y / 3 ) - 6 = 0\) | | \(4 y ^ { 3 } + 4 y ^ { 2 } - 21 y - 27 = 0\) |
| | | Use value of \(\alpha \beta \gamma\) in \(\alpha ( 1 + 1 / \alpha \beta \gamma )\) etc Correct new variable, ft on their \(\alpha \beta \gamma\) Inverse function, ft Substitute inverse function | | Complete equation including 0, any letter, any rational multiple |
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| or | \(\begin{aligned} | \Sigma \alpha = - 2 / 3 , \Sigma \alpha \beta = - 7 / 3 , \alpha \beta \gamma = 2 |
| \qquad \begin{array} { l } ( \alpha + \beta + \gamma ) \left( 1 + \frac { 1 } { \alpha \beta \gamma } \right) ( = - 1 ) |
| ( \alpha \beta + \beta \gamma + \gamma \alpha ) \left( 1 + \frac { 1 } { \alpha \beta \gamma } \right) ^ { 2 } \left( = - \frac { 21 } { 4 } \right) \end{array} |
| \qquad \alpha \beta \gamma \left( 1 + \frac { 1 } { \alpha \beta \gamma } \right) ^ { 3 } \left( = \frac { 27 } { 4 } \right) |
| \text { Hence equation is } x ^ { 3 } + x ^ { 2 } - \frac { 21 } { 4 } x - \frac { 27 } { 4 } = 0 \end{aligned}\) | | | All three correct | | Correct formula for \(\Sigma \alpha ^ { \prime }\) and substitute | | Correct formula for \(\Sigma \alpha ^ { \prime } \beta ^ { \prime }\) and substitute | | Correct formula for \(\alpha ^ { \prime } \beta ^ { \prime } \gamma ^ { \prime }\) and substitute | | Correct final equation including 0, any letter, any rational multiple |
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