trocho ::  Int -> (Int ,  Int)
trocho x	| x>=14 && mod x 3 == 0 	= (div x 3, 0)
		| x>=14 && mod x 3 == 1 	= (div (x-16) 3, 2)
		| x>=14 && mod x 3 == 2 	= (div (x-8) 3, 1)
		|otherwise 		= error "No tiene raíces reales"