180 -∠C=∠ACD

∠A+∠B=∠ACD

The second question:

Solution: The original formula = -(a+b)+ (a-c)-(b+c)-(c-b)

= -a-b+a-c-b-c-c+b

=-b-3c

Note: The first step is to change the sign of the absolute value to brackets.

A and B are both negative numbers, and their sum is also negative, so "-"is added before them.

A-c Because A is smaller than C and the result of subtraction is negative, the "-"before their brackets should be changed to "+".

B+c Because negative numbers are larger than positive numbers and their sum is negative, the "+"before their brackets should be changed to "-"

C-b is greatly reduced because C is bigger than B, and the result is positive, so the symbols before their brackets don't need to be changed.

The next two steps need no explanation.

I hope it helps you, O(∩_∩)O~