If the angles are in this order: L:M:N = 1:2:5
Let Angle l = x, then angle M = 2x and angle N = 5x
The summation of the angles is 180 degrees. That is,
x+2x+5x = 180 => 8x=180 => x (that is angle L) =180/8 = 22.5°
Angle M = 2x = 2*22.5 = 45°
Angle N = 5x =5*22.5 = 112.5°
The angles of the triangle are 22.5°, 45° and 112.5°