betas?

If two quantities are in direct proportion then the constant of proportionality is defined as their ratio $\frac{y}{x}$, or alternatively as the constant C such that $y = Cx$ where x,y are the quantities in direct proportion.

In relationships of the form $y = -kx$ with k a positive constant, the constant of proportionality is (-k) not k. (again working off y is directly proportional to x)

Edit: A refinement is needed for the first paragraph. I should specify that in my examples I am working off "y is directly proportional to x"

What does Mirin mean? :s

Hey, yes I get what you posted, so then the ratio is -y/x?

mirin you, you are perf.

What does Mirin mean? :s

Blocking your beta androceptors leads to fat gain, lethargy, low adrenaline, lack of sex drive and poor athletic performance. We should all let our inner beta run wild

In your case where you are saying a is directly proportional to -x then yes the constant of proportionality is equal to -a/x, whilst when I am saying a is dir prop to x then my constant of prop is a/x. At the end of the day we both describe the same relationship and I do understand your convention to deal only with positive constants of proportionality as this makes relationships clearer perhaps, but my relationship is still a correct one and personally I think minus signs look messy

what if you have a heart attack?

Fair enough, you made it clear.

M3 edexcel?