How many real solutions does the above equation have?
Enter 1729 if you think that there are an infinite number of solutions
Bonus : Find all these solutions.
This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try
refreshing the page, (b) enabling javascript if it is disabled on your browser and,
finally, (c)
loading the
non-javascript version of this page
. We're sorry about the hassle.
It's an really interesting problem & I'm just posting my approach of solution as I'm unsure about it.
Expanding we get ,
x + x 4 + x 9 + x 1 6 + x 2 5 = x 1 + x 4 + x 2 7 1 + x 2 5 6 + x 3 1 2 5 1
So Just transforming it into a equation by multiplying x 3 1 2 5 to both sides we have ,
f ( x ) = x 3 3 8 1 − x 3 1 5 0 − x 3 1 4 1 − x 3 1 3 4 − x 3 1 2 6 + x 3 1 2 4 + x 3 0 9 8 + 1 = 0
f ( − x ) = − x 3 3 8 1 − x 3 1 5 0 + x 3 1 4 1 − x 3 1 3 4 − x 3 1 2 6 + x 3 1 2 4 + x 3 0 9 8 + 1 = 0
Applying Descarte's Rule of sign to the polynomial we have there are two sign changes in f ( x ) i.e.
+ x 3 3 8 1 to − x 3 1 5 0 & − x 3 1 2 6 to + x 3 1 2 4
So it has atmost 2 positive real roots.
Again we have three sign changes in f(-x) i.e. ,
− x 3 1 5 0 to + x 3 1 4 1 & + x 3 1 4 1 to − x 3 1 3 4 & − x 3 1 2 6 to + x 3 1 2 4 .
So it has atmost 3 negetive real roots .
Now in f ( − x ) we have Product of roots = − a 0 a n = − − 1 1 = 1 So there are 2 or 0 negetive roots .
In the original equation we have product of roots = − 1 so we must have a negative root. The rest of the roots are complex conjugates whose product is always positive as z . z ˉ = ( ∣ z ∣ ) 2
So we have 1 + 2 = 3 real solutions.