Can the Sum of Factorials Ever be a Complete Square?

In summary, completing the square is a method used to convert a quadratic expression into a perfect square trinomial, making it easier to solve quadratic equations and find the vertex of a parabola. To complete the square, the quadratic expression must be in the form ax^2 + bx + c and the square of half the coefficient of x must be added to both sides of the equation. This allows us to create a perfect square trinomial, which is necessary for factoring and solving the equation. Completing the square can be used for all quadratic equations, but is most useful for more complex equations. It also has various real-life applications in fields such as engineering and physics.
  • #1
Karamata
60
0

Homework Statement


Proof that for [tex]n\geq 5[/tex] expression [tex]\sum_{i=1}^{n}i![/tex] can't be a complete square


The Attempt at a Solution


Mathematical induction maybe?
[tex]n=5[/tex] [tex]\sum_{i=1}^{5}i!=1+2!+3!+4!+5!=152[/tex] OK
[tex]n\rightarrow n+1[/tex] [tex]\sum_{i=1}^{n+1}i!=\sum_{i=1}^{n}i!+(n+1)![/tex]
...
One guy said that
Complete square divided by 5 can give the remains 0,1 and 4, but not 3 like here.
But, I don't understand him.

Sorry for bad English.
 
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  • #2
1+2+6+24+120 = 153 right?
subsequent factorials are all divisible by 10, so dividing by 5 will always give the remainder 3.
 

Related to Can the Sum of Factorials Ever be a Complete Square?

1. What is the purpose of completing the square?

The purpose of completing the square is to convert a quadratic expression into a perfect square trinomial. This allows us to easily solve quadratic equations and find the vertex of a parabola.

2. How do you complete the square?

To complete the square, follow these steps:
1. Make sure the quadratic expression is in the form ax^2 + bx + c.
2. Take half of the coefficient of x (b) and square it.
3. Add this value to both sides of the equation.
4. Factor the perfect square trinomial on the left side.
5. Simplify and solve for x.

3. Why do we need to add the square of half the coefficient of x?

Adding the square of half the coefficient of x allows us to create a perfect square trinomial. This is necessary in order to factor the expression and solve the equation.

4. Can completing the square be used for all quadratic equations?

Yes, completing the square can be used for all quadratic equations. However, it is most useful for equations that cannot be easily solved by factoring or using the quadratic formula.

5. Are there any real-life applications of completing the square?

Yes, completing the square has many real-life applications, such as finding the minimum or maximum value of a quadratic function, predicting the trajectory of a projectile, and solving optimization problems in engineering and physics.

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