數學題~~~很急的~~~

2007-08-22 10:48 pm

直線L:X+2Y=9穿過(A,4),求A的值.

求直線2X+3Y=7的Y軸截距.

FIND THE X-AND Y-INTERCEPT OF THE STRAIGHT LINE 2X-Y=3

已知A(1,2)和B(4,5),如果Ｐ點按1:2的比將AB分成兩份,求Ｐ點的坐標.

ABCD IS A PARALLELOGRAM. IF THE COORDINATES OF A,B AND C ARE(2,7), (6,9) AND (4,1)RESPECTIVELY,fIND THE COORDINATES of D.

回答 (2)

Gabriella Montez

2007-08-22 11:47 pm

✔ 最佳答案

( 1 ) Sub ( A,4 ) into L.

A + 2 ( 4 ) = 9

A = 1

( 2 ) Sub x = 0 into the equation.

2( 0 ) + 3Y = 7

3Y = 7

Y = 7 / 3 ( y - intercept )

( 3 ) Sub y = 0 into the equation,

2X - 0 = 3

2X = 3

X = 3 / 2 ( x - intercept )

Sub x = 0,

2( 0 ) - Y = 3

Y = - 3 ( y - intercept )

( 4 ) Let P be ( x, y ).

x = { ( 2 )( 1 ) + ( 1 )( 4 ) } / ( 2 + 1 )

= 6 / 3

= 2

y = { ( 2 )( 2 ) + ( 1 )( 5 ) } / ( 2 + 1 )

= 9 / 3

= 3

Hence P is ( 2 , 3 ).

( 5 ) As AB // CD, the slope of AB = slope of CD.

( 9 - 7 ) / ( 6 - 2 ) = ( y - 1 ) / ( x - 4 )

x - 4 = 2y - 2

x = 2y + 2 --- ( 1 )

As AC // BD, the slope of AC = the slope of BD.

( 7 - 1 ) / ( 2 - 4 ) = ( 9 - y ) / ( 6 - x )

-18 + 3x = 9 - y

3x + y = 27 --- ( 2 )

Put ( 1 ) into ( 2 ).

3 ( 2y + 2 ) + y = 27

6y + 6 + y = 27

7y = 21

y = 3

Put y = 3 into ( 1 ).

x = 2 ( 3 ) + 2 = 8

Hence D is ( 8, 3 ).

參考: My Maths Knowledge

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[匿名]

2007-08-22 10:55 pm

1.代x=a,y=4入方程,求解
2.代x=0入方程,求解

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