Explanation:
Example: -2+-5
It can also be written as -2-5.
How I do these problems, I do 2+5, which is 7. Then I add a negative sign. So -2+-5 or -2-5 is equal to -7.
-a+-b can also be written as -a-b. So yes, if a and bare negative, then a + b is also negative.
hope it helps!