If 4 tanθ =

Given:

We can picture this using the right triangle below:

Now, Using the Pythagoras Theorem i.e. \

AC = 5k

Now, Using the formula,

Putting the values in the expression, we get,

Hence, 

OR

Given:

• tan 2A = cot (A – 18°)

• 2A is Acute

We know,

Putting θ = 2A

Now, 2A is acute.

(A – 18°) and (90° – 2A) are acute.

⇒ 90° – 2A = A – 18°