急!!!中二數學!請數學的高手回答,温exam用的!!thx!!

(1)
假設正多邊為有 n 條邊。

[(2n - 4) x 90o / n] - [360o / n] = 140o
(2n - 4) x 90 - 360 = 140n
180n - 360 - 360 = 140n
40n = 720
n = 18

答：正多邊形有 18 條邊。

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(2)
x + 3y - 6 = y
x + 2y = 6 ...... (*)
3x + 6y = 18 ...... (**)

3x - 4y - 7 = y
3x - 5y = 7 ...... (***)

(**) - (***)
11y = 11
y = 1

把 y = 1 代入 (*)
x + 2(1) = 6
x = 4

答： x = 4, y = 1
=

(1) let there are n sides in the polygon,
( n - 2 ) x 180 / n - 360 / n = 140
180n - 360 - 360 = 140n
n = 18


(2) 3x-4y-7=y
y = ( 3x - 7 ) / 5
x+3y-6 =y
x - 6 = -2 ( 3x - 7 ) / 5
5x - 30 = -6x + 14
x = 4
y = 1

1)Let each 外角=x.
x+(x+140。)=180。
x=20。

Each 內角=160。

Method 1:
Let n be the no. of 邊 of 正多邊形,
180。(n-2)=160。n
n=18
Method 2:
20。n=360。 (sum of 多邊形外角)
n=18
該正多邊形有18條邊.

2) x+3y-6=y and 3x-4y-7=y
x+2y=6...(1) and 3x-5y=7...(2)
3*(1)-(2), (3x+6y)-(3x-5y)=3(6)-7
11y=11
y=1
x+2(1)=6
x=4
Therefore, x=4 and y=1.