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Mathematics

Without using trigonometric tables, evaluate the following:

sec 17°cosec 73°+tan 68°cot 22°+cos2 44°+cos2 46°.\dfrac{\text{sec 17°}}{\text{cosec 73°}} + \dfrac{\text{tan 68°}}{\text{cot 22°}} + \text{cos}^2\space 44° + \text{cos}^2\space 46°.

Trigonometric Identities

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Answer

We need to find the value of

sec 17°cosec 73°+tan 68°cot 22°+cos2 44°+cos2 46°\dfrac{\text{sec 17°}}{\text{cosec 73°}} + \dfrac{\text{tan 68°}}{\text{cot 22°}} + \text{cos}^2\space 44° + \text{cos}^2\space 46°

The above equation can be written as,

sec 17°cosec (90 - 17)°+tan 68°cot (90 - 68)°+cos2 (9046)°+cos2 46°\dfrac{\text{sec 17°}}{\text{cosec (90 - 17)°}} + \dfrac{\text{tan 68°}}{\text{cot (90 - 68)°}} + \text{cos}^2\space (90 - 46)° + \text{cos}^2\space 46°

As, cos(90 - θ) = sin θ, cosec(90 - θ) = sec θ, cot(90 - θ) = tan θ and sin2θ + cos2θ = 1. Using in above equation we get,

sec 17°sec 17°+tan 68°tan 68°+sin2 46°+cos2 46°=1+1+1=3\Rightarrow \dfrac{\text{sec 17°}}{\text{sec 17°}} + \dfrac{\text{tan 68°}}{\text{tan 68°}} + \text{sin}^2\space46° + \text{cos}^2\space46° \\[1em] = 1 + 1 + 1 \\[1em] = 3

Hence, the value of the expression is 3.

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