Quadratic polynomial can be factored using the transformation $ax^{2}+bx+c=a\left(x-x_{1}\right)\left(x-x_{2}\right)$, where $x_{1}$ and $x_{2}$ are the solutions of the quadratic equation $ax^{2}+bx+c=0$.
$$21x^{2}+5x-525=0$$
All equations of the form $ax^{2}+bx+c=0$ can be solved using the quadratic formula: $\frac{-b±\sqrt{b^{2}-4ac}}{2a}$. The quadratic formula gives two solutions, one when $±$ is addition and one when it is subtraction.
Now solve the equation $x=\frac{-5±5\sqrt{1765}}{42}$ when $±$ is plus. Add $-5$ to $5\sqrt{1765}$.
$$x=\frac{5\sqrt{1765}-5}{42}$$
Now solve the equation $x=\frac{-5±5\sqrt{1765}}{42}$ when $±$ is minus. Subtract $5\sqrt{1765}$ from $-5$.
$$x=\frac{-5\sqrt{1765}-5}{42}$$
Factor the original expression using $ax^{2}+bx+c=a\left(x-x_{1}\right)\left(x-x_{2}\right)$. Substitute $\frac{-5+5\sqrt{1765}}{42}$ for $x_{1}$ and $\frac{-5-5\sqrt{1765}}{42}$ for $x_{2}$.
