Help With Equation

A

AP1EP3

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Hi.
I am looking for help with the equation below. It's a formula for Viscosity. If T1 is assigned a value of 40 what is T2. I am a bit rusty at quadratic equations so If possible could someone give a fully worked solution from start to finish for this. I would really appreciate any help regarding this.

Calculate CSt from:
CSt=(1.37* T1)- (200/T1)
Calculate T2 from:
CSt= (4.57*T2)-(452/T2)
 
The first part is just evaluation of an expression. You'll have a number for CSt.

Then, let's write the second equation as Ax - B/x = C, where A=4.57, B=452, and C is your value of CSt.

Multiplying by x, we have Ax^2 - B = Cx, which can be rewritten as Ax^2 - Cx - B = 0.

Now look up the quadratic formula, and apply it to this equation.
 
Would someone mind posting the whole solution step by step if possible.
 
I told you enough so that if you make a fairly small effort, you can do it. Why should I do more than that for you, and leave you thinking that you are dependent on others to do ALL the math for you? You said you are "rusty"; I've put some oil on the parts, and now you have to move them a bit to spread that oil around!

If you show an attempt, then we can either tell you you're doing a good job, or help you with whatever specific errors you make. I think that's more useful to you.

To help you along, here's a link to the quadratic formula, with examples. (Actually, last time I expected the site to put in the link automatically, as it used to do.)

Of course, someone else may well decide that showing you the whole thing is appropriate, and do so.
 
Working out the quadratic formula was not an issue. I just want to confirm that I have A,B and C values correct. A = 4.57, B = 452 and C(CST) = 49.8. I consulted with someone else and they had B= -49.8 and C = -452. The solutions obtained for this quadratic equation were 16.79 and -5.89. Its nearly 20 years since I had to solve a quadratic equation so that is why I mentioned being rusty.
 
AP1EP3 said:
... I just want to confirm that I have A,B and C values correct ...
Click to expand...
Hello. If you were just looking for confirmation, then why not simply say so up front? Also, it saves time when students post their work because then we can reply with corrections right away (instead of asking to see the work).

In the standard quadratic form:

CSt = A(T2)2 + B(T2) + C

we have:

A = 4.57

B = -49.8

C = -452

We get these values by multiplying both sides of the second (given) equation by T2 and simplifying.

If you cannot find your goof, please show us what you did. Cheers

?
 
AP1EP3 said:
Working out the quadratic formula was not an issue. I just want to confirm that I have A,B and C values correct. A = 4.57, B = 452 and C(CST) = 49.8. I consulted with someone else and they had B= -49.8 and C = -452. The solutions obtained for this quadratic equation were 16.79 and -5.89. Its nearly 20 years since I had to solve a quadratic equation so that is why I mentioned being rusty.
Click to expand...
I suppose you are using A, B, and C for the a, b, and c in the standard form ax^2 + bx + c = 0. I deliberately used capital letters for my constants, because they don't mean the same thing as the formula. (Probably I should have used different letters entirely.)

Note that the quadratic equation you are solving, in my terms, was Ax^2 - Cx - B = 0 , so that we have
  • a = A = 4.57
  • b = -C = -49.8
  • c = -B = -452
So what you were told is correct. I imagine that they just told you the answer without showing the reasons.

It's so much more efficient when you tell a helper everything they might need to know from the start, so we can tell what you really need and not waste our time.
 
AP1EP3 said:
... C(CST) ...
Click to expand...
Are you thinking that C is the same as CSt? It's not.

CSt is the quadratic function's output (and T2 is its input). In other words, CSt is what they're calling y, and T2 is what they're calling x.

y = Ax2 + Bx + C

CSt = A(T2)2 + B(T2) + C

EDIT: Exponent formatting

?
 
Last edited:
Otis said:
I would have assigned my symbols b and c so that b=B and c=C.

?
Click to expand...
But when I assigned the names, it wasn't yet a quadratic equation. I just put them in place of given numbers temporarily, and to avoid having to calculate C yet.

Next time, I'll write Px - Q/x = R.
 
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