Предлагаю несколько вариантов на выбор.
а) e-f-a-b-c = -(f-e) - (a+b+c) = -(f-e+a+b+c) = -(f-e+a) - (b+c)
б) e+f-a-b+c = -(a-e-f) - (b-c) = -(a-e-f+b-c) = -(-e-f) - (a+b-c)
в) a+b+c+e+f = -(-a-b) - (-c-e-f) = -(-a-b-c-e-f) = -(-a-b-c) - (-e-f)
г) a-b+c+e-f = -(b-a) - (f-c-e) = -(b-a-c-e+f) = -(b-a-c) - (f-e)