A-LevelMathematicsTrigonometry9709/21 · Oct/Nov 2017 · Q25 Marks
Solve the equation 5 cos θ(1 + cos 2θ) = 4 for 0° ≤ θ ≤ 360°.
- Solve the equation 5 cos θ(1 + cos 2θ) = 4 for 0° ≤ θ ≤ 360°.[5]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2017). The mark or mark type is shown in brackets.
- [B1] Use cos 2θ = 2 cos² θ – 1
- [B1] Obtain 10cos³ θ = 4 or equivalent
- [M1] Use correct process to find at least one value of θ from equation of form k₁ cos³ θ = k₂
- [A1] Obtain 42.5
- [A1] Obtain 317.5 and no others between 0 and 360
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