Factorise quadratics with leading coefficient 1
key notes:
To factorize a quadratic of the form x2+bx+c, write it as
(x+r1)(x+r2)
where c=r1 . r2 and b=r1+r2.
Learn with an example
Factorise.
y2+24y+23=_______________
Look at the given quadratic:
y2+24y+23
The c term is 23, so you need to find a pair of factors with a product of 23. The b term is 24, so you need to find a pair of factors with a sum of 24. Since the product is positive (23) and the sum is positive (24), you need both factors to be positive.
Make a list of the possible factor pairs with a product of 23, and then find the one with a sum of 24.

The factors 1 and 23 have a sum of 24. Use those numbers to factorise y2+24y+23.
y2+24y+23
(y+1)(y+23)
Finally, check your work.
(y+1)(y+23)
y2+y+23y+23 Apply the distributive property (FOIL)
y2+24y+23
Yes, y2+24y+23=(y+1)(y+23).
Factorise.
j2+24j+23=_______________
Look at the given quadratic:
j2+24j+23
The c term is 23, so you need to find a pair of factors with a product of 23. The b term is 24, so you need to find a pair of factors with a sum of 24. Since the product is positive (23) and the sum is positive (24), you need both factors to be positive.
Make a list of the possible factor pairs with a product of 23, and then find the one with a sum of 24.

The factors 1 and 23 have a sum of 24. Use those numbers to factorise j2+24j+23.
j2+24j+23
(j+1)(j+23)
Finally, check your work.
(j+1)(j+23)
j2+j+23j+23Apply the distributive property (FOIL)
j2+24j+23
Yes, j2+24j+23=(j+1)(j+23).
Factorise.
n2+6n+8=_______________
Look at the given quadratic:
n2+6n+8
The c term is 8, so you need to find a pair of factors with a product of 8. The b term is 6, so you need to find a pair of factors with a sum of 6. Since the product is positive (8) and the sum is positive (6), you need both factors to be positive.
Make a list of the possible factor pairs with a product of 8, and then find the one with a sum of 6.

The factors 2 and 4 have a sum of 6. Use those numbers to factorise n2+6n+8.
n2+6n+8
(n+2)(n+4)
Finally, check your work.
(n+2)(n+4)
n2+2n+4n+8 Apply the distributive property (FOIL)
n2+6n+8
Yes, n2+6n+8=(n+2)(n+4).
let’s practice!