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anonymous
 one year ago
ques
anonymous
 one year ago
ques

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anonymous
 one year ago
Best ResponseYou've already chosen the best response.0cross sectional area of a hollow cylinder of inner radius \[x\] of thickness \[dx\] will be \[2\pi xdx??\] My attempt: dw:1442644796376:dw If we open this we get a trapezium if I'm not wrong dw:1442644914454:dw Then we apply area of trapezium formula \[A=\frac{a+b}{2}.h\]\[\therefore dA=\frac{2\pi(x+dx)+2\pi x}2{}.dx\]\[\therefore dA=(\pi(x+dx)+\pi x)dx\]\[dA=(\pi x+\pi dx+\pi x)dx\]\[dA=(2\pi x+\pi dx)dx=2\pi x dx+\pi(dx)^2\] Since dx is extremely small, (dx)^2 will be even smaller and can be ignored \[dA=2\pi x dx\]

dan815
 one year ago
Best ResponseYou've already chosen the best response.0cross sectional area if u slice it how?

IrishBoy123
 one year ago
Best ResponseYou've already chosen the best response.1or \(dA = \pi (x + dx)^2  \pi x^2 = 2 \pi x \, dx\)

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0Oh I was intrigued with opening it, I forgot about the area formula, either way the term containing (dx)^2 is ignored right

IrishBoy123
 one year ago
Best ResponseYou've already chosen the best response.1and it's brill they agree!!

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0lol, math always agrees!!

IrishBoy123
 one year ago
Best ResponseYou've already chosen the best response.1the dx^2 disappearing is the ghost of departed quantities https://en.wikipedia.org/wiki/The_Analyst
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