Question

81x^4-72x^2y^2+16y^4

Answer 1

81x^4-72x^2y^2+16y^4

=（9x^2-4y^2）^2

(3ax^n+1)(n+1连着的!）-6a^2x^n+3a^3x^n-1(连着）

=3ax^n-1(x^2-2ax+a^2)

=3ax^n-1(x+a)^2