Hey.

I was learning about how to differentiate composite functions. This is what I read:

"If y = c(ax + b) + d.

let u = ax + b, then y = cu + d.

So dy/du = c, du/dx = a, and dy/dx = ca, that is dy/dx = dy/du * du/dx

The equation dy/du = c means that y is changing c times as fast as u; similarly u is changing a times as fast as x.It is natural to think that if y is changing c times as fast as u, and u is changing a times as fast as x, then y is changing c*a times as fast as x.Thus again, dy/dx = dy/du * du/dx"

I'm not surprised that it wasn't natural for me to think that way, and even after thinking about it, I still don't understand. I just can't get my head around it! Could somebody explain

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