PSAT

System of liner equation has no solution

Two parallel lines, coefficient of one variable in one equation will match coefficient of the same variable in the other equation, BUT constants will be different. To solve just make sure both x and y coefficients are equal to each other, but not y-intercepts

system of equations with infinitely many solutions

make x and y coefficients equal to each other, y-intercepts should be different

system of equations with one solution

substitute the values at that point of intersection for x an y in the equations

When should you use substitution

when at least one coefficient of x or y is equal to 1

what is x² +2xy +y² equal to

(x+y)²

what is x² - 2xy +y² equal to

(x-y)²