Are (11 + 7) + 10 and 11 + (7 + 10) equal? Mention the property

Check the following for equality and if they are equal, mention the property: (8 - 13) xx 7 and 8 - (13 xx 7)

Check the following for equality and if they are equal, mention the property:3 xx [(-4) + (-10)] and [3 xx (-4) + 3 xx (-10)]

Verify (i) closure property (ii) commutative property (iii) associate property (iv) existence of identity and (v) existence of inverse for the opertion xx 11 on a subset A = {1 , 3 , 4 , 5 , 9} of the set of the remainders { 0 , 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10}.

If U = {4, 7, 8, 10, 11, 12, 15, 16}, A = {7, 8, 11, 12} and B = {4, 8, 12, 15}, then verify De Morgan's Laws for complementation.

The angle between the lines 2x+11y-7=0 and x + 3y + 5 = 0) is equal to