Question

Which expression is the factorization of x2 + 10x + 21?

(x + 3)(x + 7)
(x + 4)(x + 6)
(x + 6)(x + 15)
(x + 7)(x + 14)

Answer 1

Factorisation of x² + 10x + 21

• x² + 10x + 21

Here, let's first multiply the extreme values,i.e. 1*21 = 21. So, we need to get such a number that adds 21 and as we can see that 10x is the middle value of this sum. Hence, 7 and 3 is suitable as while adding it makes 10 and multiplying we get 21

• x² + (7 + 3)x + 21

• x² + 7x + 3x + 21

Now, lets segregate it into two groups. 1st group is x² + 7x and the other pair is 3x + 21 after which lets factorise them

• x(x + 7) + 3(x + 7)

• (x + 3)(x + 7)

So, we get the first option as correct which is (x + 3)(x + 7)

Answer 2

(X+3) (X+7) is the answer