Whether you are a student, engineer, or just someone who wants to be sharp with numbers, these are the formulas worth committing to memory.
Algebra
Quadratic: x = (-b ± √(b²-4ac)) / 2a
Difference of squares: a²-b² = (a+b)(a-b)
FOIL: (a+b)(c+d) = ac+ad+bc+bd
Geometry
Circle area: A = πr²
Pythagorean theorem: a² + b² = c²
Triangle area: A = ½ × base × height
Trigonometry
sin²θ + cos²θ = 1
tan θ = sin θ / cos θ
Law of cosines: c² = a² + b² - 2ab·cos(C)
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