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The short version The least common denominator (LCD) is the smallest number that every denominator in your problem divides into evenly. For 1/4 and 1/6, it’s 12. It’s the same thing as the least common multiple of the denominators. “Lowest common denominator” means exactly the same thing. Fast ways to find it: count up by…
The short version Point slope form is y – y₁ = m(x – x₁), where m is the slope and (x₁, y₁) is any point on the line. Use it when you know one point and the slope, or two points. Plug in the numbers and you’re done; no solving for b. Watch the signs….
The short version A ray in geometry is part of a line that starts at one point, called the endpoint, and goes on forever in one direction. You draw it with a dot at the endpoint and an arrow on the other end. A line gets arrows on both ends; a line segment gets none….
The short version Area is the number of unit squares that fit inside a flat shape, so the answer is always in square units (cm², ft², square units). Rectangles: length × width. Triangles: ½ × base × height. Circles: π × radius × radius. The height of a triangle or parallelogram is the straight-up distance…
The short version The range in math is the difference between the largest and smallest values in a data set: range = largest – smallest. For 14, 3, 22, 9 and 17, the range is 22 – 3 = 19. Sorting the numbers first makes the largest and smallest easy to spot. Range measures spread,…
The short version Pi (π) is the number you get when you divide any circle’s circumference (the distance around) by its diameter (the distance across). It’s the same for every circle, big or small. Pi is about 3.14, but its decimals go on forever without repeating: 3.14159265358979… That makes it an irrational number. The two…
The short version The arithmetic sequence formula is an = a1 + (n – 1)d. Plug in the first term, the common difference and the term number to get any term. The common difference d is any term minus the term before it. It can be negative when the sequence counts down. To add up…
The short version To evaluate in math means to find the value of an expression: work it out until you have a single number. If the expression has variables, replace each one with the number you’re given, then do the arithmetic. Evaluate 3x + 7 when x = 5: 3(5) + 7 = 22. Always…
The short version To multiply a fraction by a whole number, multiply the whole number by the numerator (top) and keep the denominator (bottom). Then simplify. Example: 4 × 2/3 = 8/3 = 2 2/3. If it helps, write the whole number as a fraction over 1 first: 4 = 4/1. Then multiply top by…
The short version The main types of angles are acute (less than 90°), right (exactly 90°), obtuse (between 90° and 180°), straight (exactly 180°), reflex (between 180° and 360°) and full (exactly 360°). Angles are named by how far they turn, and side length has nothing to do with it. A tiny corner and a…