Consider the difference quotient formula.

Evaluate the function at .

Replace the variable with in the expression.

The final answer is .

Find the components of the definition.

Plug in the components.

Simplify the numerator.

To write as a fraction with a common denominator, multiply by .

To write as a fraction with a common denominator, multiply by .

Write each expression with a common denominator of , by multiplying each by an appropriate factor of .

Multiply and .

Multiply and .

Reorder the factors of .

Combine the numerators over the common denominator.

Rewrite in a factored form.

Apply the distributive property.

Subtract from .

Subtract from .

Move the negative in front of the fraction.

Multiply the numerator by the reciprocal of the denominator.

Cancel the common factor of .

Move the leading negative in into the numerator.

Factor out of .

Cancel the common factor.

Rewrite the expression.

Move the negative in front of the fraction.

Find the Difference Quotient f(x)=1/(21x)