Factorisation of 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
Now, lets segregate it into two groups. 1st group is x² + 7x and the other pair is 3x + 21 after which lets factorise them
So, we get the first option as correct which is (x + 3)(x + 7)
