Solved Exercise 4 natural integers numbers

1) factorize the following expression:

a= x²-5x+4
 b= 2x²+3x-1
2) decompose 3240 and 1440 into a product of primes numbers

3) conclude a simple expression for the two numbers(the square root of 3240 and 1440)

4) k is a natural number, show that k (k +1) is an even number