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Question
In the following figure the value of cos ϕ is
Options
\[\frac{5}{4}\]
\[\frac{5}{3}\]
\[\frac{3}{5}\]
\[\frac{4}{5}\]
Solution
We should proceed with the fact that sum of angles on one side of a straight line is180°.
So from the given figure,
θ+∅+90°=180° `
So , `θ=90°-∅.............(1) `
Now from the triangle ΔABC,
`sin ∅=4/5`
Now we will use equation (1) in the above,
`sin(90°-∅)=4/5`
Therefore, `cos∅=4/5`
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