1.

Write the value of cos–1(cos 1540°).

Answer»

Given cos-1 (cos 1540°)

= cos-1{cos (1440° + 100°)}

= cos -1{cos (360° × 4 + 100°)}

We know that cos (2π + θ) = cos θ

= cos -1{cos 100°}

We know that cos-1 (cos θ) = θ if θ ∈ [0, π]

= 100°

∴ cos-1 (cos 1540°) = 100°



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