IB DP Maths: AI HL复习笔记2.3.4 Direct & Inverse Variation
Direct Variation
What is direct variation?
- Two variables are said to vary directly if their ratio is constant (k)
- This is also called direct proportion
The graphs of these models always start at the origin
How do I solve direct variation problems?
You can then use the equation to solve problems
Worked Example
b)Find the time it takes to order a list of 50 numbers.
Inverse Variation
What is inverse variation?
- Two variables are said to vary inversely if their product is constant (k)
- This is alsocalled inverse proportion
How do I solve inverse variation problems?
Exam Tip
- Reciprocal graphs generally have two parts/curves
- Only one – usually the positive – may be relevant to the model
- Think about why x/t/θ can only take positive values - refer to the context of the question
Worked Example
b)Given that the project needs to be completed within 18 hours, find the minimum number of people needed to work on it.
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