數學題(方程和不等式)

設弟弟的身高是y cm,
則小明的身高是2份之y +20

y+2份之y +20=260
y+ 2份之y+20-20=260-20
y+2份之y =240
1& 2份之1 y=240
1& 2份之1 y除1& 2份之1 y =240除1& 2份之1 y
y=160

弟弟的身高是160cm
小明的身高是160 除 2+20=100cm

You May Use The Simultaneous Linear Equation To Slove It,,

Let x Be The Height Of Xiao Ming,,

Let y Be The Height Of His Brother,,


{x+y=260.........(1)

(y/2)+20=x...........(2)

From (2),

x=(y/2)+20......(3)

Sub (3) Into (1),

(y/2)+20+y=260

(y/2)+y=240

(3y/2)=240

3y=480

y=160

Sub y=160 Into (2),

x=(160/2)+20

x=80+20

x=100

So The Height Of Xiao Ming Is 100cm.

2009-06-26 22:45:02 補充：
Yhis The The Method Of Substitution In Simultanous Equation,,

Not The Inequality.

2009-07-03 21:55:43 補充：
Corr. :

This May Use The Method Of Substitution In Simultanous Equation,,

Not The Inequality.

設小明的身高為xcm,則弟弟身高為260-xcm。
x=1/2(260-x)+20
2x=260-x+40
2x=300-x
3x=300
x=100
∴小明的身高是100cm。

設小明身高為 X cm
弟弟為 Ycm

X + Y = 260 -------- (1)
X - 20 = 0.5Y --------- (2)

From (2)
0.5Y = X - 20
Y = 2X - 40 -------- (3)

代(3)入(1)
X + (2X - 40) = 260
3X - 40 = 260
3X = 300
X = 100