Articles

Slope and distance between two points made simple. Use m = (y2 – y1) / (x2 – x1) for steepness and d = sqrt((x2 – x1)^2 + (y2 – y1)^2) for length.

Learn how to find the circumference of a circle. Use C = 2 x pi x r from the radius, or C = pi x d from the diameter, with clear worked examples.

Learn how to find the volume of a cylinder (pi x r^2 x h), a cone (one third of that), and a sphere ((4/3) x pi x r^3), with clear worked examples.

The Pythagorean theorem says a^2 + b^2 = c^2 for right triangles. Learn what it means, when to use it, and how to find a hypotenuse or a missing leg.

Learn how to find the area of any shape. Get the core idea, formulas for rectangle, square, triangle, circle, trapezoid, parallelogram, plus worked examples.

Learn how to calculate a discount and final price fast. Multiply the price by the sale rate, stack discounts the right way, then add sales tax with confidence.

Convert fractions, decimals, and percentages fast: divide top by bottom, multiply by 100, or put over 100. See the six moves plus an equivalents table.

Ratios and proportions explained simply: a ratio compares amounts as a:b, a proportion sets two ratios equal. Learn to simplify, cross-multiply, and split a total.

Learn how to calculate percentage increase and decrease with new = old x (1 + p/100), reverse it to find the original, and see why +20% then -20% never cancels.

The percentage change formula is ((new – old) / old) x 100. See why you divide by the original value, what the sign means, and worked examples.