The zero exponent rule: For any nonzero number or expression \(a\), \(a^0 = 1\).
Explanation (intuitive + formal)
Intuitively: each time you decrease an exponent by 1 you divide by the base. For example:
- \(2^3=8\), \(2^2=4\) (divide by 2), \(2^1=2\) (divide by 2), and \(2^0=1\) (divide by 2 again). The pattern forces \(2^0\) to be 1.
Formal proof using laws of exponents:
- For any \(a\neq0\) and any integer \(m\),
$$\frac{a^m}{a^m}=a^{m-m}=a^0.$$
But \(\frac{a^m}{a^m}=1\), so \(a^0=1\).
Alternate proof using logarithms (for \(a>0\)):
$$a^0=e^{0\ln a}=e^0=1.$$
Important exceptions and notes
- The rule requires the base not be zero: \(a^0=1\) only for \(a\neq0\).
- \(0^0\) is indeterminate/undefined in most contexts (algebra, arithmetic). In combinatorics it is often assigned the value 1 by convention, and in limits calculus you must examine the limiting expression because different limits can give different values.
- Negative bases work the same: \((-3)^0=1\).
- Fractional or variable bases: \(\left(\frac{1}{2}\right)^0=1\), \((5x)^0=1\) for any \(x\) with \(5x\neq0\).
Examples
- \(2^0=1\)
- \((-7)^0=1\)
- \(\left(\frac{3}{4}\right)^0=1\)
- \((5x^2)^0=1\) provided \(5x^2\neq0\) (i.e., \(x\neq0\))
- \(0^5=0\) (note: exponent positive, base zero gives 0)
- \(0^0\) — undefined / indeterminate (context-dependent)
Related points
- Negative exponents: \(a^{-n}=\frac{1}{a^n}\). The zero exponent is the border case: \(a^0=1\).
- Any product or power that ultimately equals a nonzero base to the zero power equals 1: e.g., \((ab)^0=1\) if \(ab\neq0\).
Quick practice (answers below)
- Evaluate \(3^0\).
- Evaluate \(( -2)^0\).
- Simplify \(\frac{5^3}{5^3}\).
- Is \(0^0\) equal to 1?
Answers:
- \(1\). 2. \(1\). 3. \(\frac{5^3}{5^3}=5^{3-3}=5^0=1\). 4. No — \(0^0\) is indeterminate/undefined without extra context.
Tip: Whenever you see a nonzero expression raised to the zero power, replace it with 1. Always check the base before applying the rule (make sure it isn’t zero).