問數學急 !! +15%

1. 5A=h+3AB
h=5A-3AB-----(1)
2B=h-7AB
h=2B+7AB ---(2)
(1)=(2) 5A-3AB=2B+7AB
5A=2B+10AB
=B(2+10A)
B=5A/(2+10A)

A=1, B=5(1)/(2+10)
B=5/12

2. x:(y+3)=1:2
若3x+8y=71 ,求x:y
x/(y+3)=1/2
2x=7+3 -> 6x=3y+9-----(1)
3x+8y=71 -> 6x+16y=142----(2)
(1)-(2) -16y=3yj9-142
-16y-3y=9-142
-19y=-133y
y=7
6x=3(7)+9
=21+9
x=30/6
x=5
x:y=5:7

1.
2B = h - 7AB
h = 2B + 7AB ... (1)
代 (1) 入 5A = h + 3AB
5A = 2B + 7AB + 3AB
5A = 2B + 10AB

若A = 1,
5(1) = 2B + 10(1)B
5 = 2B + 10B
5 = 12B
B = 5/12
B = 0.41666...

2.
x : (y+3) = 1 : 2
x / (y+3) = 1 / 2
2x = 1(y+3)
2x = y + 3
y = 2x - 3 ... (1)
代 (1) 入 3x + 8y = 71
3x + 8(2x - 3) = 71
3x + 16x - 24 = 71
19x = 71 + 24
19x = 95
x = 95/19
x = 5

y = 2(5) - 3
y = 7

x / y = 5 / 7
x : y = 5 : 7