Mathematical key for opposite numbers:
The opposite of a negative number is its positive number.
The opposite of a positive number is its negative number.
Therefore, the opposite of -21 is 21.
Answer:
21
Step-by-step explanation:
Opposite number or additive inverse of any number (n) is a number which, if added to n, results in 0, the identity element of addition. The opposite number for n is written as −n.
