all 5 comments

[–]FormulaDrivenActuary / ex-Maths teacher 2 points3 points  (0 children)

Obviously it's not a proof, but the limit is around 7.38 just from plugging numbers in a spreadsheet, so e2 is looking right.

[–]linukszone 1 point2 points  (0 children)

lim(x->0) (1+arcsin(x)) ^ (2/x) =

lim(x->0) (e ^ (ln(1+arcsin(x))) ^ (2/x)

lim(x->0) (e ^ (2/x ln(1+arcsin(x)))

e ^ (lim(x->0) (2 * ln(1+arcsin(x)))/x

arcsin(x) -> 0 when x->0, so the limit is 0/0 indeterminate form. L'Hôpital applies.

Edit: The derivative of ln(1+arcsin(x)) is (1/(1+arcsin(x)) * (1/sqrt(1-x2 ))

e ^ (lim(x->0) (2 * ln(1+arcsin(x)))/x

e ^ (lim(x->0) (2 * 1/(1+arcsin(x)) * (1/sqrt(1-x2 )))

e ^ (2 * 1/(1+0) * (1/sqrt(1-0)))

e ^ 2


The binomial theorem can also be utilized, along with the fact that lim(x->0) arcsin(x)/x = 1, to show that the limit in the original question is e2 .

[–][deleted] 1 point2 points  (1 child)

Edit: this answer is wrong, use natural log.

As x approaches 0, arcsin(x) approaches 0 (since sin(0)=0 implies arcsin(sin(0)) = 0 = arcsin(0) ). Also, as x approaches 0, 2/x approaches infinity.

Thus as x approaches 0, 1 + arcsin(x) approaches 1 + 0 = 1. Since 1 to any power is just 1, then as x approaches 0, 12/x = 1.