In reply to @DavidKButlerUoA
@DavidKButlerUoA Sides of the rectangle are cos(x) and sin(x).
Its area is 1/4.
So sin(x)cos(x) =1/4.
Doible angle formula: sin(2x)=2sin(x)cos(x)
So sin(2x)=1/2.
Used a calculator to find x=15°
In reply to @christianp
@DavidKButlerUoA Bits I used from memory:
When you have right-angled triangles, try making a whole rectangle.
sin(x)cos(x) has something to do with double angle formulas (had to look up if it was sin or cos)
Couldn't be bothered to work out arcsin(1/2), so used a calculator