1.5-Laws of Exponents

1.5-Laws of Exponents Important Formulae

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Grade 9 → Math → Number Systems → 1.5-Laws of Exponents

After successful completion of this topic, you should be able to:

  • Understand laws of exponents.

Exponents are a way to express repeated multiplication of a number by itself. The laws of exponents provide rules for simplifying expressions involving powers, making calculations easier. Here are the key laws of exponents:

1. Product of Powers:

When multiplying two expressions with the same base, you add the exponents:

$$ a^m \times a^n = a^{m+n} $$

For example, if $a = 2$, $m = 3$, and $n = 2$:

$$ 2^3 \times 2^2 = 2^{3+2} = 2^5 = 32 $$

2. Quotient of Powers:

When dividing two expressions with the same base, you subtract the exponent of the denominator from the exponent of the numerator:

$$ \frac{a^m}{a^n} = a^{m-n} \quad (a \neq 0) $$

For example, if $a = 5$, $m = 4$, and $n = 2$:

$$ \frac{5^4}{5^2} = 5^{4-2} = 5^2 = 25 $$

3. Power of a Power:

When raising a power to another power, you multiply the exponents:

$$ (a^m)^n = a^{m \cdot n} $$

For example, if $a = 3$, $m = 2$, and $n = 4$:

$$ (3^2)^4 = 3^{2 \cdot 4} = 3^8 = 6561 $$

4. Power of a Product:

When taking a power of a product, you distribute the exponent to each factor in the product:

$$ (a \times b)^n = a^n \times b^n $$

For example, if $a = 2$ and $b = 3$, with $n = 3$:

$$ (2 \times 3)^3 = 2^3 \times 3^3 = 8 \times 27 = 216 $$

5. Power of a Quotient:

When taking a power of a quotient, you apply the exponent to both the numerator and the denominator:

$$ \left(\frac{a}{b}\right)^n = \frac{a^n}{b^n} \quad (b \neq 0) $$

For example, if $a = 4$, $b = 2$, and $n = 2$:

$$ \left(\frac{4}{2}\right)^2 = \frac{4^2}{2^2} = \frac{16}{4} = 4 $$

6. Zero Exponent:

Any non-zero base raised to the power of zero is equal to one:

$$ a^0 = 1 \quad (a \neq 0) $$

For example:

$$ 7^0 = 1 $$

7. Negative Exponent:

A negative exponent represents the reciprocal of the base raised to the opposite positive exponent:

$$ a^{-n} = \frac{1}{a^n} \quad (a \neq 0) $$

For example:

$$ 2^{-3} = \frac{1}{2^3} = \frac{1}{8} $$

Understanding these laws of exponents is crucial for simplifying expressions and solving equations in algebra and other areas of mathematics. They provide a systematic way to handle calculations involving powers and roots.


Brigban, CC0, via Wikimedia Commons

Find:

  1. 64$^{\frac{1}{2}}$
  2. 32$^{\frac{1}{5}}$
  3. 125$^{\frac{1}{3}}$

Find:
(i) 9$^\frac{3}{2}$
(ii) 32$^\frac{2}{5}$
(iii) 16$^\frac{3}{4}$
(iv) 125$^\frac{-1}{3}$

Solution:

Calculating Exponential Expressions

The values are:

  1. 9$^{\frac{3}{2}} = (3^2)^{\frac{3}{2}} = 3^3 = 27$
  2. 32$^{\frac{2}{5}} = (2^5)^{\frac{2}{5}} = 2^2 = 4$
  3. 16$^{\frac{3}{4}} = (2^4)^{\frac{3}{4}} = 2^3 = 8$
  4. 125$^{-\frac{1}{3}} = \frac{1}{125^{\frac{1}{3}}} = \frac{1}{5} = 0.2$

Simplify:
(i) 2$^\frac{2}{3}$ $\cdot$ 2$^\frac{1}{5}$
(ii) $\left(\dfrac{1}{3^3}\right)^7$
(iii) $\dfrac{11^\frac{1}{2}}{11^\frac{1}{4}}$
(iv) 7$^\frac{1}{2}$ $\cdot$ 8$^\frac{1}{2}$

Solution:

Simplifying Exponential Expressions
The simplified forms are:
  1. 2$^{\frac{2}{3}} \cdot 2^{\frac{1}{5}} = 2^{\left(\frac{2}{3} + \frac{1}{5}\right)} = 2^{\frac{13}{15}}$
  2. $\left(\dfrac{1}{3^3}\right)^7 = \dfrac{1^7}{3^{21}} = \dfrac{1}{3^{21}}$
  3. $\dfrac{11^{\frac{1}{2}}}{11^{\frac{1}{4}}} = 11^{\left(\frac{1}{2} - \frac{1}{4}\right)} = 11^{\frac{1}{4}}$
  4. 7$^{\frac{1}{2}} \cdot 8^{\frac{1}{2}} = \sqrt{7} \cdot \sqrt{8} = \sqrt{56} = 2\sqrt{14}$