Can You Solve this Factorial Equation? | Fast & Easy Tutorial

[benjaminprevot]

Nice video 👍

One remark, the solution is correct but the demonstration contains a "mistake" (not really, just an omission 😉)

The hypothesis is X greater or EQUAL to 0.

When dividing by X, it must be indicated that X = 0 is not solution, because x! = 1 => 0² + 19x0 - 0! = 0 + 0 - 1 = -1

So the division by X is allowed.

[davidfromstow]

Fascinating problem for which you provided a very elegant solution!

[aashsyed]

You could solve very more generally, using the gamma function.

[mrmind]

Very intresting..which app are u using for the presentation?

[brunococchietto]

I have never seen this type of equation, but it's very interesting.

[mcwulf]

This is easy but what about a general method, eg when x^2 + (very large number)*X - X! = 0?

[albancal]

Maybe my question might sound a little bit off the track, but how can we be sure that y=4 or x=5 is the only solution and there isn't any other solution ?

[harantish]

what software/app are you using when writing the equation? i'd like to use the same for teaching. thanks.

[piman]

Once you put x! on the right-hand side, the only solution (as x! increases rapidly compared to x and x^2) is easily found by inspection, i.e x = 5.

[kadya]

Amazing! Let's solve more nonstandard equations like this!:)

[jamesstrickland]

There is one more solutions than just x=5, where x>0 unless we want positive integers only

[matthewkendall]

I would have arranged this as x * (x-1) ! = x^2 + 19x so (x-1)! = x + 19.
So (x-1)! > 6 = 3!
So x-1 > 3 which mean x > 4 so try x = 5 and bingo!

[mustafizrahman]

Solved it in 51 seconds. The answer is 5.