Algebra: Equations

Linear equation in one variable: ax + b = c

x = (c − b)/a

Linear equation in two variables: ax + by + c = d

Cannot be solved by itself

Pair of Linear equations in two variables: a1x + b1y + c1 = d1; a2x + b2y + c2 = d2

By substitution

Compute x in terms of y from the first equation

Substitute for x in second equation, and solve for y

Quadratic Equation: ax2 + bx + c = 0

There are 2 roots (or solutions for x):

x = [− b + √ (b2 − 4ac)] / 2a

x = [− b - √ (b2 − 4ac)] / 2a