a) \(\left(768-39\right)-768=768-39-768=768-768-39=0-39=-39\)
b)\(\left(-1579\right)-\left(12-1579\right)=\left(-1579\right)-12+1579=\left[\left(-1579\right)+1579\right]-12=0-12=-12\)
a. (768 - 39) - 768
= 768 - 39 - 768
= 768 - 768 - 39
= 0 - 39
= -39
b. (-1579) - (12 - 1579)
= (-1579) - 12 + 1579
= [(-1579) + 1579] - 12
= 0 - 12
= -12
a, (768 - 39 ) - 768
= 768 - 39 - 768
= 0 - 39
= -39
b, (-1579) - ( 12 - 1579)
= (-1579) - 12 + 1579
= [ ( -1579 ) + 1579 ] - 12
= 0 - 12
= -12