求數學問題答案(22點)

[匿名]

2013-08-10 11:58 pm

1.有大、小兩個等邊三角形，它們的邊長相差12厘米，周界之和是90厘米。求大、小兩個等邊三角形的邊長是多少。
2.有大、小兩個正方形，已知它們的邊長相差7厘米，周界之和是100厘米。大、小正方形的邊長分別是多少?

回答 (1)

Ben

2013-08-11 12:11 am

✔ 最佳答案

1.
Let x cm be the length of the big triangle,y cm be the length of the small triangle
3x+3y=90......(1)
x-y=12......(2)
From(2)
x-y=12
x=12+y......(3)
Sub x into (1)
3(12+y)+3y=90
36+3y+3y=90
6y=54
y=9
Sub y=9 into (2)
x-9=12
x=21
So the length of the big triangle is 21cm,the length of the small triangle is 9cm.
2.
Let x cm be the length of the big square,y cm be the length of the small square
4x+4y=100......(1)
x-y=7......(2)
From(2)
x-y=7
x=7+y......(3)
Sub x into (1)
4(7+y)+4y=100
28+4y+4y=100
8y=72
y=9
Sub y=9 into (2)
x-9=7
x=16
So the length of the big triangle is 16cm,the length of the small triangle is 9cm.

Hope I can help you

參考: Me

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