A de ta figure = A du carré - Aire des 2 triangles
A du carré = 54 * ( 12 + 24 ) = 54 * 36 = 1944 cm²
A du triangle du haut = (( 54 - 11 ) * ( 36 - 12 )) / 2 = ( 43 * 24 ) / 2 = 1032 / 2 = 516 cm²
A du triangle du bas = ( ( 54 - 11 ) * 12 ) / 2 = ( 43 * 12 ) / 2 = 516 / 2 = 258 cm²
A des deux triangles = 516 + 258 = 774 cm²
A de la figure = 1944 - 774 = 1170 cm²
