It is known that a > 0, b > 0, c > 0 is the largest, when a < 0 is negative, the smallest is negative two, when a > 0 is negative, the smallest is negative two, and when three is negative, the smallest is negative two.

the second question

1.x-3>0，7-x>0①=x-3+7-x=4，②=x-3-(7-x)=2x- 10

2. as shown in the figure, a < b < 0 < c, and the distance from b to the origin o is greater than c.

So b-a-c c, a -b>c < 0.

Original formula =b-a-b-c-(c-a)=-2c.

3.① when x < 1/2, the original formula is = 1-2x, and when x > 1/2, the original formula is =2x- 1 ② when X.

Third question

1. When Mn > 0, 丨 m+n 丨 m 丨+乸 n 丨

When Mn < 0 (if M > 0), divide it again.

When m+n > 0, buy m+n buy-(buy m buy n buy) = m+n-m+n = 2n < 0, so buy m+n buy.

When m+n < 0, m+n-(m+n) =-m-n-m+n =-2m < 0, so m+n.

To sum up, when Mn > 0, m-n =m-n when 丨 m+n 乸 m+ n 乸 m 0.

When m-n < 0, m-n > 0 > m-n, so m-n > m-n.