Question

fill up : (-5)+(-8)=(-8)+( ?)

Answer 1

(-5)+(-8)=(-8)+(-5) = -13

Answer 2

(-5)+(-8) becomes (-5-8) when it comes out of the first bracket. If two numbers are both with negative sign we must always add the numbers and put the minus sign before the added value.
So, it becomes -13=-8+(-13) it will be the same thing in the right hand side also . Therefore -13= -8-5
                   -13= -13
                    L.H.S.=R.H.S.