Prove the identities.
1. 5 [{cos(90 - θ)} {cos(90 - θ)}] -2 ≡ 3 - 5 [{cosθ} {cosθ}]
F.2 MAths
2007-06-03 10:20 pm
回答 (1)
2007-06-03 10:26 pm
✔ 最佳答案
5 [{cos(90 - θ)} {cos(90 - θ)}] -2 ≡ 3 - 5 [{cosθ} {cosθ}]LHS = [{cos(90 - θ)} {cos(90 - θ)}] -2
= 5 sinθ sinθ -2
= 5sin2θ – 2
= 5(1 – cos2θ) – 2
= 5 – 5cos2θ – 2
= 3 – 5cos2θ
= RHS
LHS = RHS ∴QED
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