If y = cos–1 (2x) + 2 cos–1
< x < 0, find 
.
Put 2x = cos θ
y = cos–1(cosθ) + 2cos–1(sinθ )
Considering the limits
–1 < 2x < 0
–1 < cosθ < 0
Now,
y = –π + cos–1(2x)
Differentiating w.r.t x we get
44
If y = cos–1 (2x) + 2 cos–1 < x < 0, find .
Put 2x = cos θ
y = cos–1(cosθ) + 2cos–1(sinθ )
Considering the limits
–1 < 2x < 0
–1 < cosθ < 0
Now,
y = –π + cos–1(2x)
Differentiating w.r.t x we get