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Guest Nov 12, 2018

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Generally its:

$sin^2θ + cos^2θ=1$

so $cosθ=\sqrt{1 - sin^2θ }=\sqrt{1 - \frac{4}{25} }=\sqrt{\frac{25}{25}-\frac{4}{25}}=\sqrt{\frac{21}{25}}=\frac{\sqrt{21}}{5}$

Dimitristhym Nov 12, 2018

Dimitristhym · Answer 1 · 2018-11-12T09:04:28

Generally its:

$sin^2θ + cos^2θ=1$

so $cosθ=\sqrt{1 - sin^2θ }=\sqrt{1 - \frac{4}{25} }=\sqrt{\frac{25}{25}-\frac{4}{25}}=\sqrt{\frac{21}{25}}=\frac{\sqrt{21}}{5}$

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