入吧~數學王

(2a+1) - (4a+3) = 6 OR (4a+3) - (2a+1) = 6
( 2a + 1 ) - ( 4a + 3 ) = 6
2a + 1 - 4a - 3 = 6
-2a - 2 = 6
-2a = 8
a = -4

( 4a + 3 ) - ( 2a + 1 ) = 6
4a + 3 - 2a - 1 = 6
2a + 2 = 6
2a = 4
a = 2

SO a = 2 OR a = -4

As M and N have the same y-coordinates, MN is a horizontal line.

We just consider the horizontal distance.

(2a + 1) - (4a + 3) = 6 or (4a + 3) - (2a + 1) = 6

2a + 1 - 4a - 3 = 6 or 4a + 3 - 2a - 1 = 6

-2a = 8 or 2a = 4

a = -4 or a = 2

If the distance between the two points M(2a + 1 , 0) and N(4a + 3 , 0) is 6 units, find the

two possible values of a.

By the distance formula,

√{[(4a + 3) - (2a + 1)]^2 + (0 - 0)^2} = 6

[(4a + 3) - (2a + 1)]^2 = 36

(2a + 2)^2 = 36

2a + 2 = 6 or 2a + 2 = -6

2a = 4 or 2a = -8

a =2 or a = -4

2007-02-08 19:50:43 補充：
其實亦可以根據兩點ge x 座標去計算,因為兩點都係x軸上,所以l (4a 3) - (2a 1) l = 6l 2a 2 l = 62a 2 = 6 or 2a 2 = -6a = 2 or a = -4