Add. Do not use a number line except as a check. \( -1.5+(-5.9) \)

To solve \( -1.5 + (-5.9) \), simply combine the two negative numbers. When adding negative numbers, you add their absolute values and keep the negative sign. So, \( 1.5 + 5.9 = 7.4 \), resulting in \( -7.4 \). Thus, \( -1.5 + (-5.9) = -7.4 \). When working with negative numbers, a common mistake is forgetting to keep the negative sign when adding. It's always helpful to think of moving left on the number line, but since we're not using one, just remember: more negatives mean you’re going deeper into the negative landscape!