Acute triangulations of convex quadrilaterals

An acute triangulation of a polygon ΓΓ is a triangulation of ΓΓ into acute triangles. Let f(Γ)f(Γ) denote the minimum number of triangles necessary for an acute triangulation of ΓΓ. We prove that the maximum value of f(Q)f(Q) for all convex quadrilaterals QQ is equal to 8. This solves a problem raised by Maehara (2001) in [4].