a4 - a2 - 4a2 + 4
= a2(a2 - 1) - 4(a2 - 1)
= (a2 - 1)(a2 - 4)
= (a - 1)(a + 1)(a - 2)(a + 2)
\(a^4-5a^2+4\)
\(=a^4-4a^2-a^2+4\)
\(=a^2\left(a^2-4\right)-\left(a^2-4\right)\)
\(=\left(a^2-4\right)\left(a^2-1\right)\)
\(=\left(a-2\right)\left(a+2\right)\left(a-1\right)\left(a+1\right)\)
Cách 2:
\(a^4-5a^2+4\)
= \(a^4-5a^2+5-1\)
\(=\left(a^4-1\right)-\left(5a^2-5\right)\)
\(=\left(a^2-1\right)\left(a^2+1\right)-5\left(a^2-1\right)\)
\(=\left(a^2-1\right)\left(a^2+1-5\right)\)
\(=\left(a^2-1\right)\left(a^2-4\right)\)
\(=\left(a-1\right)\left(a+1\right)\left(a-2\right)\left(a+2\right)\)
C1. a4 - 5a2 + 4
= a4 - a2 - 4a2 + 4
= a2( a2 - 1) - 4( a2 - 1)
=( a2 - 1)( a2 - 4)
= ( a + 1)( a - 1)( a - 2)( a + 2)
C2. a4 - 5a2 + 4
= a4 - 4a2 + 4 - a2
= ( a2 - 2)2 - a2
= ( a2 - 2 - a)( a2 - 2 + a)
= ( a2 + a - 2a - 2)( a2 -a + 2a - 2)
= [ a( a + 1) - 2( a + 1) ][ a( a - 1) - 2( a - 1)]
= ( a - 2)( a + 1)( a - 2)( a - 1)
Hai cách thôi nhóa
