To find the number that needs to be added to point \( c \) on the number line to make zero, we need to look at the value of \( c \). The number that should be added to \( c \) to reach zero is simply the additive inverse of \( c \).
The additive inverse of a number \( c \) is defined as the value that, when added to \( c \), results in zero. Mathematically, this can be expressed as:
\[ c + x = 0 \]
To find \( x \), we can rearrange the equation:
\[ x = -c \]
This tells us that the number that needs to be added to \( c \) to achieve zero is \( -c \).
For example:
- If \( c = 5 \), then the number to add would be \( -5 \) because \( 5 + (-5) = 0 \).
- If \( c = -3 \), then the number to add would be \( 3 \) because \( -3 + 3 = 0 \).
Thus, the answer to your question is that you need to add \( -c \) to point \( c \) to make it equal to zero.