Complex 2 variables and 2 unknown abstract question

AI Thread Summary
The discussion centers on solving two equations related to non-steady fluid mechanics: X = 122.3 (2 - Y) and Y = 0.18 * SQRT(100 + X). The provided solutions are Y = 1.903 and X = 11.82, but the poster struggles with the calculations, particularly when attempting to use the quadratic formula. They received a negative result for the b^2-4ac term, indicating a potential calculation error. Other participants confirm that the method should work and suggest re-evaluating the calculations.
EngineeringDave
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The overall question is on non steady fluid mechanics however the part on stuck on boils down to the two equations below, which I am unable to solve.

X = 122.3 (2 - Y)

Y= 0.18 * SQRT( 100 + X )

the text states the equations are satisfied by Y = 1.903 and X = 11.82.

To prove this isn't a homework I will upload a picture of the solution given.

Regards
 

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It is still like a homework question.

If you solve the first equation for Y, square both equations and set them equal, you get a quadratic equation for X. Solving this gives the solutions for Y afterwards.
 
The page its from is actually a question solution however they didn't explain how to solve that particle part.

I did as you said earlier, however, the b^2-4ac section came out negative so I was unsure I was going in the right direction.

Anyone able to advise?

Regards
 
*Particular

Sorry
 
EngineeringDave said:
however, the b^2-4ac section came out negative
Then you have a calculation error somewhere, as the approach works.
 
Since ##px^9+q## is the factor, then ##x^9=\frac{-q}{p}## will be one of the roots. Let ##f(x)=27x^{18}+bx^9+70##, then: $$27\left(\frac{-q}{p}\right)^2+b\left(\frac{-q}{p}\right)+70=0$$ $$b=27 \frac{q}{p}+70 \frac{p}{q}$$ $$b=\frac{27q^2+70p^2}{pq}$$ From this expression, it looks like there is no greatest value of ##b## because increasing the value of ##p## and ##q## will also increase the value of ##b##. How to find the greatest value of ##b##? Thanks
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