ACT® · Math: Number and Quantity
Properties of Integer Exponents
Exponent rules are just shortcuts for counting repeated factors: multiplying powers adds counts, dividing subtracts them, and that same logic forces a0 = 1 and a−n = 1/an.
Every exponent rule comes from one idea: an exponent counts how many times a base is multiplied by itself. x3 times x2 is (x times x times x) times (x times x), which is five factors of x, so you add exponents: x3+2 = x5. Dividing powers cancels shared factors, so x5 divided by x2 leaves three factors of x, matching x5-2 = x3. Raising a power to a power, like (x3)4, means four groups of three factors, which multiplies the exponents to give x12.
The zero and negative cases fall out of the same pattern instead of needing new rules. Follow the division pattern down: x3 divided by x3 is x3-3 = x0, but any number divided by itself is 1, so x0 = 1. Push one step further: x2 divided by x3 = x2-3 = x−1, and by direct cancellation that's 1/x. A negative exponent never makes the result negative. It flips the base into a fraction, 1/xn, which is small and positive.
This topic sits next to radicals and rational exponents, since x1/2 is just another case of the same counting logic applied to roots. It also connects to scientific notation, where negative exponents shrink numbers below 1. On the number and quantity items, expect these rules folded into messier expressions with coefficients and several variables, so clean handling of exponents is what keeps simplification fast and accurate.
Key terms
- Exponent
- The small number showing how many times a base is multiplied by itself.
- Negative exponent
- Shorthand for one over the positive power of the base, written a−n = 1/an.
- Zero exponent
- Any nonzero base raised to the zero power equals 1, since it matches a number divided by itself.
- Power of a power
- Raising an already-raised quantity to another exponent, which multiplies the two exponents together.
Watch it explained
- How it worksHow do the rules for multiplying, dividing and raising powers all fall out of counting factors?
- Common mistakeWhy isn't 2 to the power -3 a negative number when the exponent itself is negative?
- Worked exampleWalk me through simplifying (2x3 y)4 divided by 4x5 y2 down to a single term.
- Going furtherWhat happens to a power when the base is a fraction between 0 and 1?
Check yourself
End of topic.