基本三角學問題

sinθ - cosθ
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sinθ - 1
= √2 (sinθ (√2 / 2) - (√2 / 2) cosθ)
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sinθ - sin(π/2)
= √2 (sinθ cos(π/4) - sin(π/4) cosθ)
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2 cos(θ/2 + π/4) sin(θ/2 - π/4)
= √2 sin(θ - π/4)
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2 cos(θ/2 + π/4) sin(θ/2 - π/4)
= √2 sin(θ - π/4)
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2 sin(π/2 - θ/2 - π/4) sin(θ/2 - π/4)
= √2 sin(θ - π/4)
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2 sin(π/4 - θ/2) sin(θ/2 - π/4)
=√2 sin(π/4 - θ)
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2 sin²(π/4 - θ/2)