you have to use trigonometry. these are the trigonometric ratios:
sin x = opposite/hypotenuse
cos x = adjacent/hypotenuse
tan x = opposite/adjacent
the side labelled 15 is next to the angle, so it is the *adjacent.* the side labelled 21 is the longest side and it’s opposite the right angle of the triangle, so it’s the *hypotenuse.*
the function that involves adjacent and hypotenuse is cos.
cos x = adjacent/hypotenuse
cos x = 15/21
x= cos^-1 (15/21)
put it in your calculator and get 44 to the nearest whole.
the angle is 44