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Evaluate each of the following:(i) sin-1{(sin – 17π/8)}(ii) sin-1(sin 3)(iii) sin-1(sin 4)(iv) sin-1(sin 12)(v) sin-1(sin 2) |
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Answer» (i) Given as sin-1{(sin – 17π/8)} As we know that – sin θ = sin (-θ) So, (sin -17π/8) = – sin 17π/8 – sin 17π/8 = – sin (2π + π/8) [since sin (2π – θ) = sin (θ)] It can also be written as – sin (π/8) – sin (π/8) = sin (-π/8) [since – sin θ = sin (-θ)] On, substituting these values in sin-1{(sin – 17π/8)} we get, sin-1(sin – π/8) As sin-1(sin x) = x with x ∈ [-π/2, π/2] So, sin-1(sin -π/8) = – π/8 (ii) Given as sin-1(sin 3) As we know that sin-1(sin x) = x with x ∈ [-π/2, π/2] which is approximately equal to [-1.57, 1.57] But here x = 3, which does not lie on the above range, So, we know that sin (π – x) = sin (x) Thus, sin (π – 3) = sin (3) also π – 3 ∈ [-π/2, π/2] Sin-1(sin 3) = π – 3 (iii) Given as sin-1(sin 4) As we know that sin-1(sin x) = x with x ∈ [-π/2, π/2] which is approximately equal to [-1.57, 1.57] But here x = 4, which does not lie on the above range, So, we know that sin (π – x) = sin (x) Hence sin (π – 4) = sin (4) also π – 4 ∈ [-π/2, π/2] sin-1(sin 4) = π – 4 (iv) Given as sin-1(sin 12) As we know that sin-1(sin x) = x with x ∈ [-π/2, π/2] which is approximately equal to [-1.57, 1.57] But here x = 12, which does not lie on the above range, So, we know that sin (2nπ – x) = sin (-x) Hence, sin (2nπ – 12) = sin (-12) Here n = 2 also 12 – 4π ∈ [-π/2, π/2] sin-1(sin 12) = 12 – 4π (v) Given as sin-1(sin 2) As we know that sin-1(sin x) = x with x ∈ [-π/2, π/2] which is approximately equal to [-1.57, 1.57] But here x = 2, which does not lie on the above range, So, we know that sin (π – x) = sin (x) Thus, sin (π – 2) = sin (2) also π – 2 ∈ [-π/2, π/2] sin-1(sin 2) = π – 2 |
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