一名土木工程师正在设计一座长 131 米、高 40 米的桥梁,桥身将包含四个完全相同的抛物线拱。每个拱高 34 米,相邻两拱的底端之间相距 1 米,如图所示。建立坐标系,以第一个拱底端的左端点为原点。

- (a)
求拱 1 的 轴截距。
- (b)
表示拱 1 的方程可以写成 的形式。证明 。
- (c)
通过计算并说明,点 是否在拱 2 上。
它不会直接告诉你答案,而是问你卡在哪一步看看 AI 是怎么陪你一步步弄懂这道题的
完整解法
8(a)
1. Find the width of a single arch
Let be the width of one arch.
The total length of the bridge consists of 4 arches and 3 gaps of 1 m each.
2. Determine the $x$-intercepts of Arch 1
Since Arch 1 starts at the origin () and has a width of m, its -intercepts are at and .
and
8(b)
1. Substitute the $x$-intercepts of Arch 1 into the factored form of the quadratic equation.
From part (a), the -intercepts of Arch 1 are and .
Thus, and .
The equation is .
2. Use the maximum height of the arch to find the value of $a$.
The maximum height occurs at the midpoint of the -intercepts, which is .
The height of the arch is m, so the vertex is at .
Substitute and into the equation:
(shown)
Shown that .
8(c)
1. Determine the $x$-intercepts of Arch 1 from the context
Let the width of each arch be . There are 4 arches and 3 gaps of 1 m each.
The -intercepts of Arch 1 are and .
2. Determine the $x$-intercepts of Arch 2
Arch 2 starts after Arch 1 and a 1 m gap.
Start of Arch 2:
End of Arch 2:
The -intercepts of Arch 2 are and .
3. Form the equation of Arch 2
Since the arches are identical, the value of is the same as Arch 1, .
The equation of Arch 2 is .
4. Check if the point $(50, 30)$ satisfies the equation of Arch 2
Substitute into the equation of Arch 2:
Since , the point does not lie on Arch 2.
No, the point does not lie on Arch 2.
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