Question:
Factorise:
x2 − 9x + 20
Solution:
The given expression is $x^{2}-9 x+20$.
Find two numbers that follow the conditions given below :
Sum $=-9$
Product $=20$
Clearly, the numbers are $-5$ and $-4$.
$x^{2}-9 x+20=x^{2}-5 x-4 x+20$
$=x(x-5)-4(x-5)$
$=(x-5)(x-4)$
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