在同一个图上,画出满足下列条件的 和 的图像草图,标出轴交点。
- 和 是常数, 且 ,以及
- 图像仅有一个交点。
- (a)
写出 的最小值。
- (b)
解不等式 ,用 和 表示你的答案。
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完整解法
2(a)
1. Determine the condition for exactly one intersection by analyzing the gradients.
The graph of is V-shaped. Its right branch is defined by the line (for ) and has a gradient of .
Since the line passes through the origin and , it will naturally intersect the left branch exactly once.
To ensure there is only one point of intersection in total, must not catch up to and intersect the right branch. This requires the line to be parallel to or steeper than the right branch:
Therefore, the least possible value for is .
2(b)
1. Find the $x$-coordinate of the single point of intersection.
Based on the graphs sketched earlier, the line starts at and must intersect the left branch of the -shaped modulus graph, which has the equation .
Since it is given that there is only one point of intersection, we solve for on this branch:
2. Determine the solution to the inequality using the intersection point.
The inequality is satisfied wherever the graph of lies strictly above the line .
At , the modulus graph is at (where ), while the line is at . Thus, the modulus graph starts out above the line.
It remains above the line until they meet at the single intersection point. Since there are no other intersections, the modulus graph is only above the line to the left of this point.
Therefore, the solution is:
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