16a²-56xy+49b² does not factor. -------------------------------- However if the xy had been ab, then 16a²-56ab+49b² would have factored as (4a-7b)(4a-7b) (4x-7b)² ------------------------------------ 30x³+25x²+5y factors only by taking out common factor 5 5(6x³+5x²+y) -------------------------- However if the y had been an x 30x³+25x²+5x would become 5(6x³+5x²+1) which would become 5(3x+1)(2x+1) These problems were designed to show you that you have to be careful to look at the variables. Edwin