>>635
1/√(1-x^2)
= Σ[k=0,∞] C[-1/2,k] (-x^2)^k
= 1 + (-1/2)(-x^2) + (-1/2)(-3/2)(-x^2)^2 + o(x^4)

arcsinx = x + (1/6)x^3 + (3/20)x^5 + o(x^5)

(arcsinx)/x = 1 + (1/6)x^2 + (3/20)x^4 + o(x^4)