The distributive property
Multiply the outside factor by every term inside the brackets. This works in reverse when you factor an expression.
a(b + c) = ab + ac. For example, 3(x + 4) = 3x + 12.
Squares of sums and differences
Squaring brackets means multiplying them by themselves. Include the middle term from both cross-products.
(a + b)² = a² + 2ab + b²; (a − b)² = a² − 2ab + b².
Solve a linear equation
For ax + b = c with a ≠ 0, subtract b from both sides and divide both sides by a.
4x + 3 = 19 → 4x = 16 → x = 4.