50 Followers Problem

Find the number of solutions to following equation :

x 5 = y 9 + z 11 \large x^5 = y^9+z^{11}

where x , y , z I + x,y,z\in\mathbb{I}^+

No solutions exist 1 Infinitely many 495

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1 solution

We have x 5 = y 9 + z 11 x^5=y^9+z^{11}

Let us choose x = 2 r 1 , y = 2 11 r 2 , z = 2 9 r 2 x=2^{r_1},y=2^{11r_2},z=2^{9r_2} r 1 , r 2 , r 3 > 0 r_1,r_2,r_3>0

Substituting we get ,

2 5 r 1 = 2 99 r 2 + 2 99 r 2 2^{5r_1}=2^{99r_2}+2^{99r_2}

2 5 r 1 = 2 99 r 2 + 1 \implies 2^{5r_1}=2^{99r_2+1}

5 r 1 = 99 r 2 + 1 \implies 5r_1=99r_2+1 , it is sufficient to prove that there are infinitely many integers ( r 1 , r 2 ) (r_1,r_2) which satisfy this relation. Suppose r 2 = 10 k + 1 r_2=10k+1 where k [ 1 , ) k\in[1,\infty) is any integer.

5 r 1 = 990 k + 100 r 1 = 198 k + 20 \implies 5r_1=990k+100\implies r_1=198k+20

So there are infinitely many solutions of the form ( x , y , z ) = ( 2 198 k + 20 , 2 11 ( 10 k + 1 ) , 2 9 ( 10 k + 1 ) ) (x,y,z)=(2^{198k+20},2^{11(10k+1)},2^{9(10k+1)}) where k ( 0 , ) k\in(0,\infty) is an integer.

Really nice one ...... I haven't thought that

Sayandeep Ghosh - 5 years, 1 month ago

What does the bold I mean?

Joe Mansley - 3 years, 8 months ago

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