Need help in Aptitude Question

WBahn

Joined Mar 31, 2012
32,823
|| sign for parallel an what this mean |x| ?
i have studied it is for +ve value.
It really depends on what 'x' is, but generally it means something related to "the size of x". If x is just a number, the |x| is the absolute value of x, or simply the "positive" version of x. If x is a vector, the |x| is the magnitude of the vector. If x is a set, then |x| is the cardinality of the set, which just means the number of items in the set. If x is a string, then |x| means the length of the string. I'm sure there are many other uses, but the common theme is that it is a positive number that captures the notion of the "size" of x.
 

Thread Starter

RRITESH KAKKAR

Joined Jun 29, 2010
2,829
So, Rpq=Rp'q'
Rp'q' = "1 Ω + (1 Ω || Req) + 1 Ω"


Rpq= 1+.75+1=2.75

If Ro is the resistance between P' and Q' (in the right half of the bottom figure), then what is the resistance, Req, between P and Q. This is a problem that you have already solved. Req is the series sum of two resistors of resistance R plus a third resistor, of resistance R, that is in parallel with Ro. Use that to write an equation for Req in terms of R and Ro.

Rpq is not just the resistance of the three resistors that we split off. Rpq IS the same resistance as Rp'q'.

Merely write an algebraic equation for: 1Ω ||Req=Req-2Ω

1Ω x Req / 1+Req = Req-2
Req =( Req - 2)(1+Req)




 

WBahn

Joined Mar 31, 2012
32,823
Merely write an algebraic equation for: 1Ω ||Req=Req-2Ω

1Ω x Req / 1+Req = Req-2
Req =( Req - 2)(1+Req)
So close! (and, if you are willing to abuse units and the rules of mathematics -- which you obviously are -- then you got it).

1Ω x Req / 1Ω+Req = Req-2Ω

This addresses the units, and is even dimensionally sounds, but is not correct because you are forgetting order of operations. Because multiplication/division are done before addition/subtraction, what you have here is really

((1Ω x Req) / 1Ω) + Req = Req-2Ω

That's not what you intended, but it IS what you wrote. One of your biggest problems has been sloppiness with the math. You need to work on being consistently correct in your presentation of math expressions. What you meant to write was

(1Ω x Req) / (1Ω + Req) = Req - 2Ω

The next step, which you carried out successfully (ignoring units) is

(1Ω x Req) = (Req - 2Ω)(1Ω + Req)

Now just multiply everything out and solve for Req.
 
Top