Make x the subject of y(x^2+a^2)=a^3

**BabyMilo** · May 12th 2009, 10:51 AM

Many Thanks!

**HallsofIvy** · May 12th 2009, 11:14 AM

Originally Posted by BabyMilo

Many Thanks!

You want to solve $y(x^2+ a^2)= a^3$ for a.

Okay, multiplying the left side, $x^2y+ a^2y= a^3$ which is the same as $a^3- ya^2- x^2y= 0$ . That is a cubic equation and there is a formula for the solution- unfortunately, it is very complicated.

Look at Cubic Formula -- from Wolfram MathWorld

**BabyMilo** · May 12th 2009, 11:21 AM

I appreciate your help! But I am just making x the subject (like rearranging the equation). Many Thanks!

**mr fantastic** · May 12th 2009, 07:51 PM

Originally Posted by BabyMilo

I appreciate your help! But I am just making x the subject (like rearranging the equation). Many Thanks!

Divide by y. Subtract a^2. Take the square root.

**BabyMilo** · May 12th 2009, 10:56 PM

Originally Posted by mr fantastic

Divide by y. Subtract a^2. Take the square root.

so would it be? x=sq root of (a^3/y)-a^2 Many THanks!

**mr fantastic** · May 13th 2009, 01:34 AM

Originally Posted by BabyMilo

so would it be? x=sq root of (a^3/y)-a^2 Many THanks!

You need $\pm \sqrt{}$

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