Can you solve this system of equations with four variables?

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In summary, "find all real solutions" refers to finding all possible values of a variable that make an equation or inequality true, using algebraic techniques such as factoring or the quadratic formula. An equation can have multiple real solutions, especially in cases involving quadratic or cubic terms, but it is important to carefully consider all possible values and check for accuracy. Special cases to consider include even powers and variables in the denominator, which may result in two solutions or extraneous solutions.
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anemone
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Find all real solutions to the following system of equations:

$a+b+c+d=5$

$ab+bc+cd+da=4$

$abc+bcd+cda+dab=3$

$abcd=-1$
 
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  • #2
Solution that I saw somewhere online:

We're given

$a+b+c+d=5$

$ab+bc+cd+da=4$

$abc+bcd+cda+dab=3$

$abcd=-1$

Let $X=a+c$ and $Y=b+d$. Then the system of equations is equivalent to

$x+Y=5$

$XY=4$

$Xbd+Yac=3$

$(Xbd)(Yac)=-4$

The first two of these equations imply $(X,\,Y)=(1,\,4)$ and the last two give $(Xbd,\,Yac)=(4,\,-1)$.

And this yields:

$X$$Y$$Xbd$$Yac$$(a,\,c)$$(b,\,d)$
144-1$\dfrac{1\pm 2}{2}$2
14-14--
414-1--
41-142$\dfrac{1\pm 2}{2}$
 

1. What does "find all real solutions" mean?

"Find all real solutions" refers to finding all possible values of a variable that make an equation or inequality true. These values must be real numbers, meaning they can be positive, negative, or zero.

2. How do I find all real solutions?

To find all real solutions, you must first rearrange the equation or inequality so that the variable is isolated on one side. Then, you can use algebraic techniques such as factoring or the quadratic formula to solve for the variable. It is important to check your solutions by plugging them back into the original equation to ensure they make the equation true.

3. Can an equation have more than one real solution?

Yes, an equation can have multiple real solutions. This is especially common in equations involving quadratic or cubic terms. It is important to carefully consider all possible values and check your solutions to ensure you have found all real solutions.

4. How do I know if I have found all real solutions?

If you have carefully followed the steps to isolate the variable and solved for it correctly, you should have found all real solutions. To be sure, you can plug your solutions back into the original equation and see if they make the equation true.

5. Are there any special cases to consider when finding all real solutions?

Yes, there are a few special cases to consider when finding all real solutions. One is when the equation or inequality has an even power, which may result in two solutions (if positive) or no solutions (if negative). Another is when the equation or inequality has a variable in the denominator, which may result in extraneous solutions. It is important to be aware of these special cases and carefully check your solutions to ensure they are all real.

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