Show that a 4 </msup> + b 4

Jaqueline Kirby

Jaqueline Kirby

Answered question

2022-06-15

Show that a 4 + b 4 + ( a + b ) 4 2 is a perfect square.

Answer & Explanation

iceniessyoy

iceniessyoy

Beginner2022-06-16Added 27 answers

If a 4 + 2 a 3 b + 3 a 2 b 2 + 2 a b 3 + b 4 is a square, it has to be of the form ( x a 2 + y a b + z b 2 ) 2 for some coefficients x , y , z
Then a 4 + 2 a 3 b + 3 a 2 b 2 + 2 a b 3 + b 4 = x 2 a 4 + 2 x y a 3 b + ( y 2 + 2 x z ) a 2 b 2 + 2 y z a b 3 + z 2 b 4
Comparing coefficients we get x 2 = 1 , 2 x y = 2 , y 2 + 2 x z = 3 , 2 y z = 2 , z 2 = 1
Solving this system we get x = y = z = 1 and x = y = z = 1, so a 4 + 2 a 3 b + 3 a 2 b 2 + 2 a b 3 + b 4 = ( a 2 + a b + b 2 ) 2

Do you have a similar question?

Recalculate according to your conditions!

Ask your question.
Get an expert answer.

Let our experts help you. Answer in as fast as 15 minutes.

Didn't find what you were looking for?