Differentiate sin−1(1+x22x)
Let u=1+x22x.
u′=(1+x2)22(1−x2),1−u2=(1+x2)2(1−x2)2 dxd[sin−1(u)]=1−u2u′=1+x2∣1−x2∣(1+x2)22(1−x2)=1+x22⋅∣1−x2∣1−x2
So,
y′=1+x22for ∣x∣<1;y′=−1+x22for ∣x∣>1;undefined at x=±1
(Using the identity sin−1(1+x22x)=2tan−1x on ∣x∣<1 gives y′=1+x22 immediately.)

























