Question: Factorise:
y2 − 6y − 135
Solution:
The given expression is $y^{2}-6 y-135$.
Find two numbers that follow the conditions given below:
Sum $=-6$
Product $=-135$
Clearly, the numbers are $-15$ and $9 .$
$y^{2}-6 y-135=y^{2}-15 y+9 y-135$
$=y(y-15)+9(y-15)$
$=(y-15)(y+9)$
