cc
aire totale du rectangle MNPQ = AN x MQ = a x k
et
aire MRSQ = MR x MQ = (a-b) x k
aire RNPS = RN x MQ = b x k
comme aire MRSQ = aire totale - aire RNPS
on aura
(a-b) x k = a x k - b x k
soit
k (a-b) = ka - kb
