How many numbers

are reciprocal of themselves?

two: + 1 and - 1

Step-by-step explanation:

If a number is equal to its own reciprocal, it will satisfy the equation ...

x = 1/x

Multiplying by x and subtracting 1 gives ...

x^2 - 1 = 0

This factors as ...

(x - 1) (x + 1) = 0

By the zero product rule, the solutions are those values of x that make one or more factors zero:

x = 1

x = - 1

There are two self-reciprocals.