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Mathematics

If sin θ = 610\dfrac{6}{10}, find the value of cos θ + tan θ.

Trigonometrical Ratios

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Answer

Given,

sin θ=610sin2 θ=361001cos2 θ=36100cos2 θ=136100cos2 θ=10036100cos2 θ=64100cos θ=64100cos θ=810tan θ=sin θcos θ=610810=68.\Rightarrow \text{sin θ} = \dfrac{6}{10} \\[1em] \Rightarrow \text{sin}^2 \text{ θ} = \dfrac{36}{100} \\[1em] \Rightarrow 1 - \text{cos}^2 \text{ θ} = \dfrac{36}{100} \\[1em] \Rightarrow \text{cos}^2 \text{ θ} = 1 - \dfrac{36}{100} \\[1em] \Rightarrow \text{cos}^2 \text{ θ} = \dfrac{100 - 36}{100} \\[1em] \Rightarrow \text{cos}^2 \text{ θ} = \dfrac{64}{100} \\[1em] \Rightarrow \text{cos θ} = \sqrt{\dfrac{64}{100}} \\[1em] \Rightarrow \text{cos θ} = \dfrac{8}{10} \\[1.5em] \text{tan θ} = \dfrac{\text{sin θ}}{\text{cos θ}} \\[1em] = \dfrac{\dfrac{6}{10}}{\dfrac{8}{10}} = \dfrac{6}{8}.

Substituting values in cos θ + tan θ we get,

cos θ + tan θ =810+68=32+3040=6240=3120=11120\text{cos θ + tan θ }= \dfrac{8}{10} + \dfrac{6}{8} \\[1em] = \dfrac{32 + 30}{40} \\[1em] = \dfrac{62}{40} \\[1em] = \dfrac{31}{20} \\[1em] = 1\dfrac{11}{20}

Hence, cos θ + tan θ = 11120.1\dfrac{11}{20}.

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