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k(k + 5)
It is because 3 is a factor of 9. So if 9 is a factor of some number X, then X = k*9 for the factor pair 9 and k But X = k*9 = k*(3*3) = (k*3)*3 so that X is k*3 times 3 ie it is a multiple of 3.
7k^(2) + 7k - 140 Factor out '7' Hence 7(k^(2) + k - 20) Factor inside the brackets 7(k + 5)(k - 4) Done!!!!
k = 5
Consider a number k. Let m be the square root of k : since k is not a square number, m is not an integer and so m cannot be a factor of k.Suppose p is a factor of k and suppose p< m.Then k has another factor q such that k = p*q and since p < m, then q> m.Thus, for every factor smaller than the square root, there is another factor that is larger than the square root. That is, the factors come is distinct pairs and so there is an even number of factors.