Remember: SOH-CAH-TOA
Sine (of an angle!) = opposite / hypotenuse
We're looking at angle M here, to find the sine of M. Looking from angle M, the side that is opposite is NO and the hypotenuse is MO.
sin(M) = NO / MO = NO / 13
We do not know NO, but we can use the Pythagorean theorem to find NO because this is a right triangle.
Pythagorean theorem: a^2 + b^2 = c^2
---a and b are legs of the triangle, c is the hypotenuse
12^2 + b^2 = 13^2
144 + b^2 = 169
b^2 = 25
b = 5
NO = 5
sin(M) = NO / MO = 5 / 13
Answer: sin(M) = 5 / 13
Hope this helps!
