Prove the identity tan²x - sin²x = tan²x sin²x.
- Prove the identity tan²x - sin²x = tan²x sin²x.[4]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2010). The mark or mark type is shown in brackets.
- [M1] LHS = sin²x/cos²x - sin²x
- Replace t² by s²/c² or sec² – 1
- [M1] sin²x(1 – cos²x)/cos²x
- Use of 1 - cos²x = sin²x
- [M1] sin²x sin²x / cos²x
- Valid overall method
- [A1] tan²xsin²x AG
- OR RHS = sin²x/cos²x . sin²x
- [M1] Replace t² by s²/c2
- [M1] sin²x(1 – cos²x)/cos²x
- Use of 1 - cos²x = sin²x
- [M1] (sin²x/cos²x) - sin²x
- Valid overall method
- [A1] tan²x - sin²x AG
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