2 1.-4

The square of (cd+ 1) will not be negative, and the absolute value of a+b will not be negative, so they are all equal to zero. So cd equals-1, a+b equals zero, and the answer is -4.

22.

2 or-1

Let's not talk about the process of this question ~

23.

-2a-b

The absolute value of b is equal to -b, the absolute value of -b-a is equal to -b+a, and the absolute value of a+b is equal to-b-a. The formula is converted into:

-b-(-b+a)+(-b-a)=-b+b-a-b-a =-2a-b

24.

45

Angle AOC = 90, DOB= AOD, COE= EOB. Suppose we draw an angle with light OD as one side and equal to angle DOC in the angle AOD, and then divide the rest equally, we can get: angle AOC = 2 doc+2 coe = 90°, angle doe= angle DOC+ angle Coe = half angle AOC = 90°/2 = 45°.

25.

-(-2) to the n power.

Because there are positive numbers and negative numbers in this column, when n is odd, this number is positive, and when n is even, this number is negative. The absolute values of these numbers are all powers of 2. When the exponent n of -2 is odd, this number is negative, plus the negative sign, it becomes positive. When the exponent n of -2 is even, this number is positive, and adding a negative sign becomes negative, which is in line with the meaning of the question. So the answer is:

-(-2) to the n power.