Question

Which of the following is x⁴ + y⁴ identically equal to?

Answer 1

$x^4+y^4 \\ \\x^4= (x^2)^2, y^4 = (y^2)^2 \\ \\x^4- y^4= (x^2)^2 - (y^2)^2 = (x^2 + y^2)(x^2 - y^2 )\\ \\now \ you \ can \ factor \ the \ second \ again \\ \\(hopefully \ you \ see \ that \ it's \ a \ difference \ of \ squares): \\ \\x^4 - y^4= (x^2 + y^2)(x + y)(x - y) \\ \\Answer : \ (A) \ (x^2 + y^2)(x + y)(x - y) \\ \\ \\ a^2-b^2 =(a-b)(a+b)$