Problems need HardWork #21

Find the number of pairs of integer solutions :

x 3 + y 4 = 7 x^3 + y^4 = 7


The answer is 0.

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1 solution

Gokul Kumar
Sep 2, 2015

j u s t t a k e m o d 13 W h a t a r e t h e c o n g r u e n c e s o f t h i r d p o w e r s ? 0 , 15 , 8 , 12 W h a t a r e t h e c o n g r u e n c e s o f f o u r t h p o w e r s ? 0 , 1 , 3 , 9 t h e r e i s n o p a i r w h i c h c a n g i v e u s 7 m o d 13 H e n c e , t h e r e a r e n o i n t e g r a l s o l u t i o n s t o t h i s e q u a t i o n just\ take\ mod13 \\ What\ are\ the\ congruences\ of\ third\ powers? \\ 0,15,8,12 \\ What\ are\ the\ congruences\ of\ fourth\ powers? \\ 0,1,3,9\\ there\ is\ no\ pair\ which\ can\ give\ us\ 7\ mod13 \\ Hence,\ there\ are\ no\ integral\ solutions\ to\ this\ equation

How do I know which number to take as a modulus to prove the existence of integer solution?

찬홍 민 - 5 years, 9 months ago

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i f t h e r e i s a e q u a t i o n l i k e x a + y b = k , a n d i f ( a b + 1 ) i s p r i m e y o u s h o u l d t a k e m o d ( a b + 1 ) if\ there\ is\ a\ equation\ like\ { x }^{ a }+{ y }^{ b }=k, \\ and\ if\ \left( ab+1 \right) is\ prime\, you\ should\ take\ mod\left( ab+1 \right)

Gokul Kumar - 5 years, 9 months ago

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Why is that so??

Bala vidyadharan - 5 years, 6 months ago

I didn't understand. What did you mean ny congruence of a power?

Rajat Pandey - 5 years, 9 months ago

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l i k e t a k i n g c u b e s o f n u m b e r s a n d t h e n f i n d i n g w h a t r e m a i n d e r i t g i v e s w h e n d i v i d e d b y 13 A n d t h e n s i m i l a r l y f o r t h e f o u r t h p o w e r s like\ taking\ cubes\ of\ numbers\ and\ then\ finding\ what\ remainder\ it\ gives\\ when\ divided\ by\ 13 \\ And\ then\ similarly\ for\ the\ fourth\ powers

Gokul Kumar - 5 years, 9 months ago

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