Prove the identity 1/cos θ - cos θ/(1 + sin θ) = tan θ.
- (i)Prove the identity 1/cos θ - cos θ/(1 + sin θ) = tan θ.[4]
- (ii)Solve the equation 1/cos θ - cos θ/(1 + sin θ) + 2 = 0 for 0° ≤ θ ≤ 360°.[3]
Mark scheme
Marking points from the official mark scheme (May/June 2014). The mark or mark type is shown in brackets.
- [M1] Correct addition of fractions
- [M1 M1] LHS = (1+s-c²)/(c(1+s)) = (s²+s)/(c(1+s)) Use of s²+c²=1. (1+s)cancelled.
- [A1] = tan θ → answer given.
- [M1] Uses part (i). Allow tan θ = –2
- [A1 A1] θ = 116.6° or 296.6° Co. √ for 180°+ and no other solutions in the range.
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