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Given: cos 9 = sin and 9<90° i.e. 9α is an acute angle

And we know that, sin(90°-θ) = cos θ by property.

So, we can write cosine in terms of sine using this property,

cos 9 = sin (90°-)

Thus, sin (90°-9) = sin (cos 9 = sin(90°-9) & sin(90°-) = sin )

90°-9 =

10 = 90° (By rearranging)

= 9°

We have got the value of i.e. = 9°

Putting it in tan 5, we get

tan 5 = tan (5.9) = tan 45° = 1

, tan 5 = 1

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