Factorise:

$x^4-13x^2+36$

Factorise:

$x^2+3xy-88y^2$

If $x^4-x^2{y}^2-72y^4=(x+py)(x-qy)\left(x^2+r{y}^2\right)$, then find the value of $p+q+r$.

Factorise:

$a^3{b}^3-9a^2{b}^2+20ab$

The factorised form of ${\left(x^2+x\right)}^2+4\left(x^2+x\right)-21$ is of the form $\left(A+B+C\right)\left(A+B-D\right)$. What is the value of $C+D$?

Factorise:

$2x^2+3x+1$

Factorise:

$3x^2+17x+10$

Factorise: $5x^2+9x-2$

Factorise:

$6x^2-7x-5$