數學問題 (10點)

1.-8, x, y. 7

7-y = y-x .... (1)

y-x = x-(-8)
y-x = x+8 .... (2)

from (2)

y-8 = 2x
x = (y-8)/2

sub into (1)

7-y = y - (y-8)/2
14 - 2y = 2y - y + 8
14 - 8 = 2y - y + 2y
6 = 3y
y = 2

sub into ( y-8 = 2x )
2-8 = 2x
-6 = 2x
x = -3

-8, -3, 2, 7



2013-12-01 16:18:06 補充：
2. x/5 = y/x = 320/y

x² = 5y ..... (1)

y² = 320x .... (2)

from (1)

y = x²/5

sub into (2)

x⁴/25 = 320x

x³ = 8000

x = 20

y = 80

2013-12-01 17:07:53 補充：
The series is 5, 20, 80, 320