\(a^4+a^2-2\)
\(=a^4-a^3+a^3-a^2+2a^2-2a+2a-2\)
\(=a^3\left(a-1\right)+a^2\left(a-1\right)+2a\left(a-1\right)+2\left(a-1\right)\)
\(=\left(a-1\right)\left(a^3+a^2+2a+2\right)\)
\(=\left(a-1\right)\left[a^2\left(a+1\right)+2\left(a+1\right)\right]\)
\(=\left(a-1\right)\left(a+1\right)\left(a^2+2\right)\)
=a^2-1+a^4-1
=a2-1+(a2-1)(a2+1)
=(a2-1)(a2+2)
Ta có a4 + a2 - 2 = a4 - a2 + 2a2 - 2
= (a4 - a2) + (2a2 -2)
= a2( a2 - 1) + 2(a2 - 1)
= (a2 + 2) (a2 -1)
= (a2 +2 )(a - 1)(a + 1)
