Let

Dividing numerator and denominator with cos²x, we have

Put tan x = t

⇒ sec²x dx = dt (Differentiating both sides)

When x = 0, t = tan 0 = 0

When x = , t = tan = ∞

So, the new limits are 0 and ∞.

Substituting this in the original integral,

Multiplying numerator and denominator with 3, we have

Now, we can write

Substituting this in the original integral,

Recall