Question
Solve the equation
(x+2)^4+(x+1)^4=97
Solve the equation
(x+2)^4+(x+1)^4=97
Noticed the prime number 97 is equal to the sum of the fourth power of 2 and the fourth power of 3
97 = 16+81=2^4+3^4
The equation is equivalent to
(x+2)^4+(x+1)^4=2^4+3^4
[(x+2)^4-2^4]+[(x+1)^4-3^4]=0
Use the difference of squares formula,
[(x+2)^2-2^2][(x+2)^2+2^2]+[(x+1)^2-3^2][(x+1)^2+3^2]=0
Continue to use the difference of squares formula,
x(x+4)(x^2+4x+8)+(x-2)(x+4)(x^2+2x+10)=0
Since there's a common factor x+4 in the both terms, we get the first solution
x=-4
Now let's continue for other solutions. Factor out the common factor as it will not be 0 for other solutions.
x(x^2+4x+8)+(x-2)(x^2+2x+10)=0
x^3+4x^2+8x+x^3+2x^2+10x-2x^2-4x-20=0
2x^3+4x^2+14x-20=0
x^3+2x^2+7x-10=0
Since x=1 is one of the solutions of the equation, we will factor the equation aiming to use x-1
x^3-1+2x^2-2+7x-7=0
(x-1)(x^2+x+1+2x+2+7)=0
(x-1)(x^2+3x+10)=0
Then we get
x=1
or
x=\dfrac{-3\pm\sqrt{9-40}}{2}=\dfrac{-3\pm i2\sqrt{10} }{2}
In summary, the equation has two real solutions and two imaginary solutios.