In problem #577679, the question says if two of the medians of triangle ABC are perpendicular, then .... ($5a^2 = b^2 + c^2$, the result).
In the course of solving it, I drew the following picture (slightly different to that question).
I found that angle ABC 'must be obtuse' before I can get a satisfactory (hand) drawing. (I did not use any tool from Wolfram.)
My statement is "Prove or disprove the triangle must be obtuse under the mentioned given".
I tried to use the cosine law to show that $cos ABC$ (or $a^2 + c^2 - b^2$) is negative, but was not successful.