Trigonometry question

[AngloScot]

What exactly does arc sin mean? If 'a rough plane is inclined at arc sin 7/25 to the horizontal' does this mean that the opposite vector to the angle is 7 and the hypotenuse is 25?

[Tweed]

It is the inverse of sin. Sometimes written as sin-1. So as sin = opp/hyp, the sin of the angle is 7/25, i.e Sin(A) = 7/25. The arc sin of 7/25 will get you the answer A,(approx 16 deg.) The opposite and hypotenuse doesn't necessarily = 7 and 25, it could be any multiple, i.e. 14 and 50, etc.

[LeedsRhinos]

Spooky. Tweed took the words right out of my mouth!!

[LeedsRhinos]

Not!

[Tweed]

...just to add, we're not necessarilly talking triangles here, the hypotenuse and plane could go on infinately, but if you drop a perpendicular (to the plane) from any point on the hypotenuse, the ratio will always be the same, i.e. 7/25, where 7 is the opp, and 25 is the hyp.