Math help?

here is the question:





22. state whether the quanitity has a direct variation.





The Circumference C if a circle and it's diameter d are related by the equation C=(pie symbol)d.





ok i have no idea my math teacher didnt explain this to me. can you help me understand better.

Math help?
direct variation is when both things increase or decrease at the same time. y/x = constant or y = kx





since C = pi D and pi is a constant. C and D are direct variants.
Reply:If two variables have a direct variation, it means that one element directly affects the other. So, in other words, if you change d, it changes C in the same direction. So, if I increase d, C increases as well. And yes, this is a direct variation. As the diameter of a circle increases, the circumference of the circle increases as well, in direct proportion with the diameter.
Reply:Yes, direct variation. When the value d increases, the value C also increases.


The opposite of direct variation is inverse variation where one value increases and the other decreases.
Reply:Yes there is a direct variation. This means one varies linearly with the other i.e. if you double the diameter of a circle, the circumference doubles. Any equations of the type y=kx have a direct variation, in other words (dividing both sides by x) the expression y/x is always constant, with the value k.

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