Question

1.已知点C和D是线段AB上的两个点,且AB=a,CD=b(a不等于b）,M和N分别是AC和BD的中点,求MN的长.

Answer 1

1.MN = MC + CD + DN

=( MC + DN ) + CD

=( AB - CD )/ 2 + CD

=( a - b )/ 2 + b

=(a + b)/2

2.A+1的绝对值=A+1,则A>=-1

2A+3的绝对值=-2A-3,则A