Use a number line to find the sum.$-1+(-8)$

To add two numbers with similar signs, add their absolute values and keep the similar sign with the resulting number.

To add two numbers with opposite signs, subtract the absolute value of smaller number from absolute value of larger number and keep the sign of larger number with the resulting number

To add two numbers using a number line, start from the first number on the number line and move to right side if the second number is positive or to the left side if the second number is negative.

To evaluate the sum $-1+(-8)$, start from the first number –1 on the number line. Since the second number is negative, so move to the left side 8 units on the number line as shown below,

On moving 8 units to left side from –1, we reach at the point $-9$.

Thus, the value of the given sum is $-9$.