892
1) 4 + (-8) = - 4 - ответ
2) 50 + (-20) = 30 - ответ
893
1) -3 + 2 = - 1 и 5 + (-3) = 5-3 = 2 и -7 + 5 = -2
2) -2 + 2 = 0 и 0 + (-4) = - 4 и 8 + (-2) = 8-2 = 6
4sin15sin75-1=4(cos(15-75)-cos(15+75))/2-1=2(cos(-60)-cos90)-1=2(1/2-0)-1=2*1/2-1=0