O-LevelAdditional MathematicsTrigonometry4037/11 · May/June 2020 · Q1012 Marks
Show that 1/(sec θ - 1) - 1/(sec θ + 1) = 2 cot² θ.
- (a)(i)Show that 1/(sec θ - 1) - 1/(sec θ + 1) = 2 cot² θ.[3]
- (a)(ii)Hence solve 1/(sec 2x - 1) - 1/(sec 2x + 1) = 6 for -90° < x < 90°.[5]
- (b)Solve cosec(y + π/3) = 2 for 0 ≤ y ≤ 2π radians, giving your answers in terms of π.[4]
Mark scheme
Marking points from the official mark scheme (May/June 2020). The mark or mark type is shown in brackets.
- [M1] For dealing with the fractions
- [M1] For use of the correct identity
- [A1] Al for given answer, must see 8 / tan^2θ first
- [M1] M1 for use of (i) and attempt to simplify
- [A1] tan 2x = ± 1/√3
- [M1] M1 for attempt to solve, may be implied by one correct solution
- [A2] Al for each pair of correct solutions
- [M1] For dealing with cosec and an attempt to solve
- [M1] M1 for a complete method of solution, may be implied by a correct solution
- [A1] y = π/2
- [A1] y = 11π/6
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