Good day, while reading up on an elementary math study book, i have encountered that a proof is build upon the following (see attachment for the figure). Are the Areas CDE and BED really the same? I tried to calculate this from abstraction, not sure where I could have made a mistake.. g1 is the falling diagonal, g2 the rising, referenced to the start (0,0), the intercepts c1 is yielded when g1(x=b); c2 when g2(x=0). The formula for the area is constructed via (two triangles at the points: [C-(b,c1)-D) and (b,c1)-D-E]) the other vice versa): CDE: (h-c1)*b*0.5 + 0.5*h*r*m - 0.5*c1*r*m BDE: (h-c2)*b*0.5 + 0.5*h*r - 0.5*c2*r I made the whole figure and the formula, so it could all be wrong! Although I calculated the intercepts with the drawn perpendicular and they came out correct with quite a big figure and m number, I think the rug is in the surface area formula.. Also upon rough calculation I think formula for BED is correct! so CDE must be revisited!! Thank you for your response!