☰ Contents · Algebra

Properties of powers with a natural exponent

Lessons 13 · 1 lessons · Sh.A. Alimov, O.R. Xolmuhamedov, M.A. Mirzaahmedov. Algebra, Grade 7, revised and expanded 5th edition. O‘qituvchi NMIU, Tashkent, 2017
13

Properties of powers with a natural exponent

Textbook: pp. 59–67
GoalKnow the properties of powers and use them to compute and simplify.
New words
powers with the same base · bir xil asosli darajalarpower of a power · darajani darajaga ko‘tarishpower of a product · ko‘paytmani darajaga ko‘tarishpower of a fraction · kasrni darajaga ko‘tarish
Explanation

Powers with a natural exponent have five properties. 1) aᵐ · aⁿ = aᵐ⁺ⁿ: when multiplying powers with the same base, the exponents are added. 2) aᵐ : aⁿ = aᵐ⁻ⁿ (m > n, a ≠ 0): when dividing, the exponents are subtracted. 3) (aᵐ)ⁿ = aᵐⁿ: raising a power to a power multiplies the exponents. 4) (ab)ⁿ = aⁿbⁿ: raising a product to a power raises each factor to that power. 5) (a/b)ⁿ = aⁿ/bⁿ (b ≠ 0): the numerator and denominator are raised separately. These properties follow from the definition of a power: for instance, a² · a³ = (a · a) · (a · a · a) = a⁵. We also use them in the reverse direction: 2³ · 5³ = (2 · 5)³ = 1000.

Worked examples
5³ · 5⁴ = 5⁷; 7⁹ : 7⁶ = 7³ = 343; (a⁴)³ = a¹².
25⁴ · 4⁴ = (25 · 4)⁴ = 100⁴ = 10⁸. Using property 4 in reverse made the computation very easy.
Class activity

“Power dominoes”: each card has an expression on one half (a³ · a⁴) and a result on the other (a⁷). Pupils link the cards into a correct chain.

Practice
1
Compute 2⁷ : 2⁴.
2
Write a⁵ · a³ · a² as a single power.
3
Compute (3²)³.
4
Why does the property aᵐ : aⁿ = aᵐ⁻ⁿ require m > n?