To solve simple quadratic equations you need to be able to factorise quadratic expressions, like x²+9x +20
To do this look for a pair of numbers that add up to 9 and muliply together to make 20.
If you can’t find the right pair, write down all the pairs of factors of 20.
1 x 20
2 x 10
4 x 5
Now we can see the correct pair is 4 and 5.
So x²+9x +20=(x+4)(x+5)
Check this by multiplying out the brackets.
Lets try one involving negative numbers.
x² -x -12
The pairs of factors of -12 are
-12 x 1
-6 x 2
-4 x 3
-3 x 4
-2 x 6
-1 x 12
The pair that add up to -1 (because there is -x in the expression) are -4 and 3
So x² -x -12=(x-4)(x+3)