\(81x^4+4=\left(9x^2\right)^2+36x^2+4-36x^2\)
\(=\left(9x^2+2\right)^2-\left(6x\right)^2=\left(9x^2-6x+2\right)\left(9x^2+6x+2\right)\)
81x4 + 4
= 81x4 + 36x2 + 4 - 36x2
= ( 81x4 + 36x2 + 4 ) - 36x2
= ( 9x2 + 2 )2 - ( 6x )2
= ( 9x2 - 6x + 2 )( 9x2 + 6x + 2 )
81x4 + 4
= (9x2)2 + 22
= ( 9x2 + 2 )( 9x2 - 2 )
\(81x^4+4=\left(9x^2\right)^2+36x^2+4-36x^2=\left(3x^2+2\right)^2-\left(6x\right)^2\)
\(=\left(3x^2+2-6x\right)\left(3x^2+2+6x\right)\)