# what are these

Joined Feb 10, 2016
68
Its my exams next week I took a look at the previous paper and i found this section in it can anyone please tell me what i have to study in order to complete this section please help me.

#### kubeek

Joined Sep 20, 2005
5,731
A schoool of some sort would definitely help.

Joined Feb 10, 2016
68
I asked my professor about this but he was not willing to tell me anything and in class he doesn't tell us anything at all #### kubeek

Joined Sep 20, 2005
5,731
Fisrst is an exponential equation, the second two are from trigonometry, both basic high school math.

Joined Feb 10, 2016
68
so what would be the time constant of this exponential equation

#### kubeek

Joined Sep 20, 2005
5,731
This being a homework forum, try showing some effort on your side. You need to find out what that exponential equation is and then solve it.

Joined Feb 10, 2016
68
it is not a homework problem i dont know anything about it.so tell me what is it so i can study about it and be prepared for the finals.i searched exponential equation but no luck

#### kubeek

Joined Sep 20, 2005
5,731

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Joined Feb 10, 2016
68
so how would i be able to find the time constant and yeh 2 other questions what i have to study which topic what i would write in search engines to find this type of things.

#### WBahn

Joined Mar 31, 2012
26,068
it is not a homework problem i dont know anything about it.so tell me what is it so i can study about it and be prepared for the finals.i searched exponential equation but no luck
It doesn't matter whether it is an actual, explicit homework problem. In this forum YOU are expected to at least make an honest attempt to solve the problem. We will not spoon feed you solutions just because you claim that it is not an assigned problem.

If you really have absolutely no idea what an exponential equation is or what a time constant is or how they relate to each other, then you need to drop this class and retake the prerequisite course(s).

#### WBahn

Joined Mar 31, 2012
26,068
All the cutouts look like a radius from the soldered pins to keep isolation distance. But that trace looks to be completely ignoring that.
Huh???   #### WBahn

Joined Mar 31, 2012
26,068
This being a homework forum, try showing some effort on your side. You need to find out what that exponential equation is and then solve it.
How about trig identities? Step functions?

Joined Feb 10, 2016
68
ok ill tell you what i know so far we get exponential decay when capacitor or inductor is discharging e^-t/tao in this question they have given us the decay of 70.7 percent when t=0 and we have to find it when its in t=5 second so do can i do this when e^-0tao=70.7 and now e^-5/tao
thats i know so far .

#### WBahn

Joined Mar 31, 2012
26,068

Joined Feb 10, 2016
68
find the time constant which decay to 70.7 we have to find tao in 5 second does it means e^-5/tao=70.7 am i close ?

#### WBahn

Joined Mar 31, 2012
26,068

(Find the time constant) (of an exponential function) (which decays to 70.7% (of its initial value at t = 0) in 5 msec).

Joined Feb 10, 2016
68
v=e^-1 =0368 means 36.8 percent
so i need a value of tao to make 70.7 percent

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#### kubeek

Joined Sep 20, 2005
5,731
Huh???   sorry that was meant to go to another thread.
And to be true, I think this thread was somewhere else than homeworks when I first replied to it.

#### WBahn

Joined Mar 31, 2012
26,068
sorry that was meant to go to another thread.
Figured it was something like that -- but had to jerk your chain a bit. And to be true, I think this thread was somewhere else than homeworks when I first replied to it.
Very possible.

#### WBahn

Joined Mar 31, 2012
26,068
v=e^-1 =0368 means 36.8 percent
so i need a value of tao to make 70.7 percent
First things first.

You have an exponentially decaying function.