In the right triangle, the side opposite angle-'y' is 4 units long,
and the hypotenuse is 20 units long.
When I say "opposite" and "hypotenuse", does it ring a bell ?
In a right triangle, the quotient of (opposite side)/(hypotenuse)
is the sine of the acute angle. So in this particular right triangle,
the sine of angle-'y' is 4/20 or 0.200 .
If you look up the angle whose sine is 0.2 in a book or on your
calculator, or just go online and search "arcsin 0.200", the angle
you get will be angle 'y'.
