The triangle QPR having inscribed triangle STU will allow the artisan to divided his glass piece into four equal triangular pieces.
In order to divide an equilateral triangle into four equal triangular glass pieces, the artisan must;
Since the triangle is equilateral,
PQ = QR = RP
Mid-point divides the lines into equal parts. So,
PS = SQ = QU = UR = RT = TP
Thus, it is proved that
ΔPST = ΔSTU = ΔTUR = ΔQSU
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