Use one of the basic laws of exponents to understand how negative exponents work. The rule is x^m / x^n = x^(m - n). This means that if the exponent in the denominator is larger than the exponent in the numerator, the exponent will be negative. For example, x^3 / x^4 = x^(3 - 4) = x^(-1). So x^(-1) = 1/x. Similarly, x^(-2) = 1/x^2 and x^(-3) = 1/x^3. To check this out with some numbers, 2^3 / 2^4 = 8/16 = 1/2. Applying the rule, 2^3 / 2^4 = 2^(-1) = 1/2. You can use the rule x^m / x^n = x^(m - n) to understand how to deal with negative exponents anywhere in a rational expression.
Simplify the effect of a negative exponent in the numerator with the following rule: "Move an expression with a negative exponent in the numerator down to the denominator by making the negative exponent positive." One easy way to see this rule is illustrated when you look at 1 / x^k if you want to get rid of the fraction. Remembering that anything to the zero power is one, you have 1 / X^k = x^0 / x^k = x^(0 - k) = x^(-k).
See what happens to negative exponents in the denominator with the following algebraic derivation: 1/x^(-k) = 1/(1/x^(k)) = (x^k/x^k)(1/(1/x^(k))) = x^k /(x^k/x^k) = x^k / 1 = x^k. This means that the rule for getting rid of negative exponents in the denominator can be expressed as: "Move an expression with a negative exponent in the denominator up to the numerator by making the negative exponent positive." Even more concisely: "When you move an expression with an exponent across the fraction bar, the sign of the exponent changes."