Question
Solve the equation
(x+2)^4+x^4 = 82
Solve the equation
(x+2)^4+x^4 = 82
This equation is a special form of quartic equation. Noticed 82 is the sum of 81 and 1. 81 is the fourth power of 3 and 1 is the fourth power of 1.
(x+2)^4+x^4 = 82 = 81+1
(x+2)^4-1 = 9^2-x^4
[(x+2)^2+1][(x+2)^2-1]=(9-x^2)(9+x^2)
Since both sides contain a common factor x+3, we get one of the solutions of the function
x = -3
Factor out the common factor, (1) is simplified to the equation
(x^2+4x+5)(x+1) = (3-x)(9+x^2)
x^3+4x^2+5x+x^2+4x+5 = 27+3x^2-9x-x^3
Combine the like terms and simplify, we get
Noticed if we substitute 1 to x, the left hand side is
1^3+1^2+9\times 1-11=0
Therefore x=1 is another solution of the equation
Let's factor the equation (2) considering the factor of x-1
x^3-1+x^2-1+9x-9=0
(x-1)(x^2+x+1+x+1+9)=0
(x-1)(x^2+2x+11)=0
It's found that the equation has one real number and 2 imaginary numbers
x=1
or
x = \dfrac{-2\pm i\sqrt{40} }{2} =-1\pm i\sqrt{10}
In summary, the equation has 4 solutions - 2 real numbers and 2 imaginary numbers