Question

factorise y² - 10 y + 25​

Answer 1

$y^2-10y+25$

$=y^2-2y\cdot \:5+5^2$

$\mathrm{Apply\:Perfect\:Square\:Formula}:\quad \left(a-b\right)^2=a^2-2ab+b^2$

$a=y,\:b=5$

$=\left(y-5\right)^2$