Originally Posted by
Soroban .
Example: $\displaystyle 6x^2 - 35x + 36$
Write the two pairs of parentheses and "split the x's": .$\displaystyle (\;x\qquad)(\:x\qquad)$
Use the first coefficient twice: . $\displaystyle (\overbrace{6x}^\downarrow\qquad)(\overbrace{6x}^\ downarrow\qquad)$
Multiply the first coefficient by the last coefficient: .$\displaystyle 6 \times 36 \,=\,216$
We will factor $\displaystyle 216$ into two parts.
Note the sign of the last term.
. . If "+", think sum.
. . If "-", think difference.