Algebra essentials
A linear equation has the form a x plus b equals c. Solve it by moving b to the other side, then dividing by a. For example, 2x plus 3 equals 11 gives 2x equals 8, so x equals 4.
To expand a x plus b times c x plus d, multiply every term in the first bracket by every term in the second, then combine like terms.
Geometry without diagrams
The area of a triangle is one half times base times height. The area of a rectangle is length times width. The area of a circle is pi times radius squared.
The angles inside any triangle add up to 180 degrees. The angles inside a quadrilateral add up to 360 degrees. Knowing these totals lets you find a missing angle by subtraction.
Introduction to trigonometry
In a right angled triangle, sine of an angle equals the opposite side divided by the hypotenuse. Cosine equals the adjacent side divided by the hypotenuse. Tangent equals opposite divided by adjacent.
A helpful memory phrase is SOH CAH TOA: Sine is Opposite over Hypotenuse, Cosine is Adjacent over Hypotenuse, Tangent is Opposite over Adjacent.