If 
x > 0, prove that 
Put x = tan θ
Considering the limits
0 < x < ∞
0 < tan θ < ∞
Now,
y = 2θ + 2θ
y = 4θ
y = 4tan–1x
Differentiating w.r.t x we get
39
If x > 0, prove that
Put x = tan θ
Considering the limits
0 < x < ∞
0 < tan θ < ∞
Now,
y = 2θ + 2θ
y = 4θ
y = 4tan–1x
Differentiating w.r.t x we get