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anemone
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Find the sum of all real numbers $a$ such that $5a^4-10a^3+10a^2-5a-11=0$.
anemone said:Find the sum of all real numbers $a$ such that $5a^4-10a^3+10a^2-5a-11=0$.
zzephod said:[sp]$$P(a)=5a^4-10a^3+10a^2-5a-11=5(q^2-1)^2+5(a^2-a)-11$$[/sp]
...and the rest is but "sound and fury signifying nothing"
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topsquark said:Hey! I actually know how to do this one! Wheeee!
\(\displaystyle 5 a^4 - 10 a^3 + 10 a^2 - 5 a - 11 = 0\)
This is a quartic equation, so let's do what we all do when presented by such a polynomial equation: Get rid of the cubic term. (Well, okay, the second thing anyway. I suspect the first thing to do is go to Wolfram|Alpha to get the answer and work backward.)
Anyway, let a = b + 1/2.
\(\displaystyle 5 \left ( b + \frac{1}{2} \right )^4 - 10 \left ( b + \frac{1}{2} \right )^3 + 10 \left ( b + \frac{1}{2} \right )^2 - 5 \left ( b + \frac{1}{2} \right ) - 11 = 0\)
Expanding out and simplifying reveals we also get to get rid of the linear term:
\(\displaystyle 5b^4 - \frac{5}{2}b^2 - \frac{191}{16} = 0\)
Solving this I get
\(\displaystyle b = \pm\sqrt{ -\frac{1}{4} \pm \frac{7 \sqrt{5}}{10} }\)
\(\displaystyle a = \pm \sqrt{ -\frac{1}{4} \pm \frac{7 \sqrt{5}}{10} } + \frac{1}{2}\)
(Note: The two +/- are unrelated.)
Now, list all the possible values of a (not all real) and add them all up.
\(\displaystyle \text{Sum of a} = \left ( \sqrt{ -\frac{1}{4} + \frac{7 \sqrt{5}}{10} } + \frac{1}{2} \right ) + \left ( i \cdot \sqrt{ \frac{1}{4} + \frac{7 \sqrt{5}}{10} } + \frac{1}{2} \right ) + \left ( - \sqrt{ -\frac{1}{4} + \frac{7 \sqrt{5}}{10} } + \frac{1}{2} \right ) + \left ( -i \cdot \sqrt{ \frac{1}{4} + \frac{7 \sqrt{5}}{10} } + \frac{1}{2} \right )\)
\(\displaystyle = 4 \cdot \frac{1}{2} = 2\)
=-Dan
MarkFL said:Perhaps you mean:
[sp]$$P(a)=5a^4-10a^3+10a^2-5a-11=5\left(a(a-1)\right)^2+5a(a-1)-11$$[/sp]
Now you are set to finish...
topsquark said:Hey! I actually know how to do this one! Wheeee!
\(\displaystyle 5 a^4 - 10 a^3 + 10 a^2 - 5 a - 11 = 0\)
This is a quartic equation, so let's do what we all do when presented by such a polynomial equation: Get rid of the cubic term. (Well, okay, the second thing anyway. I suspect the first thing to do is go to Wolfram|Alpha to get the answer and work backward.)
Anyway, let a = b + 1/2.
\(\displaystyle 5 \left ( b + \frac{1}{2} \right )^4 - 10 \left ( b + \frac{1}{2} \right )^3 + 10 \left ( b + \frac{1}{2} \right )^2 - 5 \left ( b + \frac{1}{2} \right ) - 11 = 0\)
Expanding out and simplifying reveals we also get to get rid of the linear term:
\(\displaystyle 5b^4 - \frac{5}{2}b^2 - \frac{191}{16} = 0\)
Solving this I get
\(\displaystyle b = \pm\sqrt{ -\frac{1}{4} \pm \frac{7 \sqrt{5}}{10} }\)
\(\displaystyle a = \pm \sqrt{ -\frac{1}{4} \pm \frac{7 \sqrt{5}}{10} } + \frac{1}{2}\)
(Note: The two +/- are unrelated.)
Now, list all the possible values of a (not all real) and add them all up.
\(\displaystyle \text{Sum of a} = \left ( \sqrt{ -\frac{1}{4} + \frac{7 \sqrt{5}}{10} } + \frac{1}{2} \right ) + \left ( i \cdot \sqrt{ \frac{1}{4} + \frac{7 \sqrt{5}}{10} } + \frac{1}{2} \right ) + \left ( - \sqrt{ -\frac{1}{4} + \frac{7 \sqrt{5}}{10} } + \frac{1}{2} \right ) + \left ( -i \cdot \sqrt{ \frac{1}{4} + \frac{7 \sqrt{5}}{10} } + \frac{1}{2} \right )\)
\(\displaystyle = 4 \cdot \frac{1}{2} = 2\)
=-Dan
zzephod said:It now reads as I had intended, not quite sure how the transcription error could have occurred in the form that it did.
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Finding the sum of all real numbers means adding up every possible real number. This includes positive and negative integers, fractions, decimals, and irrational numbers such as pi or square root of 2. It is an infinite sum that never ends.
No, it is not possible to find the exact sum of all real numbers. This is because the set of real numbers is infinite, and we cannot add an infinite number of numbers. We can only approximate the sum by using computational methods or mathematical formulas.
The value of the sum of all real numbers is undefined or infinite. Since the sum is infinite and never-ending, we cannot assign a specific value to it. It is often represented by the symbol ∞, which means infinity.
The concept of the sum of all real numbers is used in various mathematical concepts and formulas, such as the Riemann zeta function and the Euler-Mascheroni constant. It is also used in calculus and number theory to understand the behavior of infinite sums and series.
No, there is no single formula that can be used to calculate the sum of all real numbers. However, there are some mathematical formulas that can be used to approximate the sum, such as the Euler-Mascheroni constant and the zeta function. These formulas involve complex mathematical concepts and are used mainly for theoretical purposes.