Grade 8 · Math

Grade 8 math

Grade 8 math gets your child ready for high school: the Pythagorean theorem, lines and slope, exponents and square roots. Here is what it covers, where kids usually get stuck, and one way to help.

What your child learns this year

Every curriculum words it differently, but most grade 8 classes cover the same ground:

The Pythagorean theorem. Finding a missing side of a right triangle.
Linear relations. Tables, graphs and equations of straight lines, and what the slope means.
Exponents and roots. Powers, square roots, and very big or very small numbers in scientific notation.
Equations. Solving equations with the letter on both sides (and pairs of equations in the US).
Geometry. Surface area and volume of cylinders and other solids, and angle rules.
Data. Scatter plots and lines of best fit, and choosing the right graph.

Where kids usually get stuck

1Adding the squares when a leg is missing. When the long side is known, you subtract. Adding gives a leg longer than the long side, which can't happen.
2Ignoring the brackets on a negative. (−3)² is 9, because −3 × −3 = 9. But −3² is −9: only the 3 is squared.
3Counting the wrong way in scientific notation. 0.00042 is 4.2 × 10⁻⁴, not 10⁴: a small number gets a negative power.

One of Pip's tricks

Legs squared add up to the long side squared

Use it when a missing side on a right triangle, like legs of 6 and 8.

Find the hypotenuse: the side across from the square corner, always the longest.
Missing hypotenuse: square both legs, add, then take the square root.
Missing leg: square the hypotenuse, subtract the other leg squared, then take the square root.

Watch it work. Legs of 6 and 8. 6 × 6 = 36 and 8 × 8 = 64. 36 + 64 = 100, and the square root of 100 is 10. The hypotenuse is 10.

Why it works: the squares drawn on the two short sides have exactly the same area as the square on the long side, for every right triangle there is.

Try three

Have a go, then tap to see the answer.

1.A right triangle has legs of 5 cm and 12 cm. How long is the hypotenuse?
Show the answer
13 cm. 25 + 144 = 169, and the square root of 169 is 13.
2.A right triangle has a hypotenuse of 10 cm and one leg of 6 cm. How long is the other leg?
Show the answer
8 cm. The long side is known, so subtract: 100 − 36 = 64, and the square root of 64 is 8.
3.What is (−3)²?
Show the answer
9. The brackets mean −3 × −3, and a negative times a negative is positive.

How Sparkpip fits in

Pip, Sparkpip's tutor, works through problems like these with your child one small step at a time, using tricks like the one above.

Start free See how it works

Your curriculum

Sparkpip is built on the grade 8 math curriculum for your province or state. The official pages:

Also: Grade 7 math · Grade 9 math · Grade 8 science · Grade 8 English