Consider the expression [tex]x^2-\dfrac{36}{42}x-7x^2.[/tex]
This expression contains two terms with [tex]x^2,[/tex] group them:
[tex]x^2-7x^2=x^2(1-7)=-6x^2.[/tex]
Now simplify term [tex]\dfrac{36}{42}x=\dfrac{6}{7}x.[/tex]
Now [tex]x^2-\dfrac{36}{42}x-7x^2=-6x^2-\dfrac{6}{7}x=6\left(-x^2-\dfrac{1}{7}x\right)=-6x\left(x-\dfrac{1}{7}\right).[/tex]
This expression is defined for all x.
