Question 15904
a + a = a ; site an example 3 + 2= 5 adding at the same sign will give u the sum and copy the common sign

-a + a = (-3)+2=-1 and 2+(-3)=-1 adding a different sign will give u a subtaction and copy the sign which has a bigger value

(-a)-(-a)=(-a)+a site an example(-3)-(-2)= (-3)+2=-1 copy the first given value and change the minus sign into plus sign then change the second value to the opposite sign 



(-a)-a=(-a)+(-a) copy the first given and change the minus sign into plus sign then change the second value to the opposite sign

(-a)*(-a)=a; multiply the same sign will give as positive value

(-a)*a=(-a); multiply unlike sign will give you negative value