Here's how to factor the quadratic expression x² - 11xy - 12y²:
**1. Find the Factors of the Coefficient on the y² term:**
* The coefficient on the y² term is -12. Find two numbers that multiply to -12 and add up to the coefficient on the xy term (-11).
* The numbers 1 and -12 satisfy this condition: (1)(-12) = -12 and (1) + (-12) = -11
**2. Rewrite the Expression:**
* Replace the -11xy term with the two terms using the factors we just found:
x² - 11xy - 12y² = x² + xy - 12xy - 12y²
**3. Factor by Grouping:**
* Factor out a common factor from the first two terms and a common factor from the last two terms:
x(x + y) - 12y(x + y)
* Notice how now (x + y) has become a common factor.
**4. Factor out the Common Factor:**
(x + y)(x - 12y)
**Therefore, the factored expression is (x + y)(x - 12y)**