Edexcel IGCSE Maths 复习笔记 2.12.1 Direct & Inverse Proportion
Edexcel IGCSE Maths 复习笔记 2.12.1 Direct & Inverse Proportion
What is proportion?
- Proportion?is a way of talking about how two?variables?are related to each other
- Direct?proportion: as one variable goes?up?the other goes up by the same?factor
eg. If one variable is multiplied by 3, so is the other
- Inverse?proportion: as one variable goes up the other goes?down?by the same?factor
eg. If one variable is multiplied by 3, the other is?divided?by 3
You should know what the graphs look like:
How do we deal with proportion questions?
- Identify the two?VARIABLES?(called?A?and?B?below)
- Choose?TYPE?of proportion:
A?is?DIRECTLY?proportional to?B?use formula?A = kBA?is?INVERSELY?proportional to?B?use formula?A = k÷B
- FIND?k?using the values given in the question
- Write?FORMULA?for?A?in terms of?B?(using your value of?k)
- USE?formula to find the required quantity
Exam Tip
Even if the question doesn’t ask for a formula (Step 4. above) it is always worth working one out and using it in all but the simplest cases.
Worked Example
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