check the picture below.
a rhombus has a few features, the diagonals meet at right-angles, that means angle 1 is clearly a right-angle.
because the rhombus is just a slanted square, namely, even though it's slanted, the sides are all equal in length, and because of that, the angles on the 2 locations, will be smaller than the angles at the 3 locations.
since the rhombus has 4 congruent triangles, we can check any of those, keeping in mind that the sum of their interior angles must be 180°. So whatever ∡2 and ∡3 are, they must add up to 90, and ∡2 being the smaller one.
so 90° and 41° and 49°, gives us 90 + 41 + 49 = 180.
