You can put this solution on YOUR website! SEE THE TRAPEZOID ....ABCD below
AREA OF TRAPEZOID IS GIVEN BY
AREA=(1/2)*ALTITUDE*(SUM OF PARALLEL SIDES)=(1/2)*DA*(AB+CD)
WHERE ALTITUDE IS THE PERPENDICULAR DISTANCE BETWEEN PARALLEL SIDES =DA
PARALLEL SIDES ARE AB AND CD.
IN THE SAME FIGURE IF WE CONSIDER TRIANGLE.....ABD... AREA OF TRIANGLE IS GIVEN BY....AREA=(1/2)*BASE*ALTITUDE =(1/2)*AB*DA
WHERE ALTITUDE IS PERPEDICULAR HEIGHT FROM ONE VERTEX SAY D TO BASE AB THAT IS DA IN THIS FIGURE.