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2a2b2+2a2c2+2b2c2-a4-b4-c4
=4a2b2-(a4+2a2b2+b4)+(2b2c2+2a2c2)-c4
=2(ab)2-(a+b)2+2c2(a2+b2)+c4
=2(ab)2-[(a+b)2-2c2(a2+b2)+c4]
=2(ab)2-(b2+a2-c2)2
=[(a+b)2-c2][-(a-b)2+c2]
=(a+b-c)(a+b+c)(c-a+b)(a+c-b)
\(2a^2b^2+2a^2c^2+2b^2c^2-a^4-b^4-c^4\)
\(=4a^2b^2-\left(a^4+2a^2b^2+b^4\right)+\left(2b^2c^2+2a^2c^2\right)-c^4\)
\(=2\left(ab\right)^2-\left(a+b\right)^2+2c^2\left(a^2+b^2\right)+c^4\)
\(=2\left(ab\right)^2-\left[\left(a+b\right)^2-2c^2\left(a^2+b^2\right)+c^4\right]\\ =2\left(ab\right)^2-\left(b^2+a^2-c^2\right)^2\)
=\(\left[\left(a+b\right)^2-c^2\right]\left[-\left(a-b\right)^2+c^2\right]\\ =\left(a+b+c\right)\left(a+b+c\right)\left(c-a+b\right)\left(a+c-b\right)\)
a ) 2a2b2 + 2b2c2 + 2a2c2 - a4 - b4 - c4
= 4a2b2 - 2a2b2 + 2b2c2 + 2a2c2 - a4 - b4 - c4
= 4a2b2 - ( a4 + 2a2b2 + b4 ) + ( 2b2c + 2a2c2 ) - c4
= 4a2b2 - [ ( a2 + b2 ) - 2.c2. ( b2 + a2 ) + c4 ]
= ( 2ab )2 - ( a2 + b2 - c2 )
= ( 2ab - a2 - b2 + c2 )( 2ab + a2 + b2 - c2 )
= [ c2 - ( a2 - 2ab + b2 ) ] . [ (a2 + 2ab + b2 ) - c2 ]
= [ c2 - ( a - b )2 ] . [ ( a + b )2 - c2 ]
= ( c - a + b )( c + a - b )( a + b - c )( a + b + c )
b ) x2 - 10x + 24
= ( x2 - 10x + 25 ) - 1
= ( x - 5 )2 - 12
= ( x - 5 - 1 )( x - 5 + 1 )
= ( x - 6 )( x - 4 )
a)=(a2+2ab+b2) +(b2-c2) +(ab+ac)-c2
=(a+b)2 -c2 +(b+c)(b-c) +a(b+c)
=(a+b-c)(a+b+c)+(b+c)(a+b-c)
=(a+b-c)(a+2b+2c)
c)a4+2a3+1
=a4 +a3+a3+a2-a2-a+a+1
=a3(a+1)+a2(a+1)-a(a+1)+(a+1)
=(a+1)(a3+a2-a+1)
d)x5+x+1
=(x5+x4+x3)-x4-x3-x2+x2+x+1
=x3(x2+x+1) -x2(x2+x+1) +(x2+x+1)
=(x2+x+1)((x3-x2+1)
e)x8+x4+1
=(x4)2 +2x4+1-x4
=(x4+1)2 -x4
=(x4+1+x2)(x4+1-x2)
=(x4+2x2+1-x2)(x4-x2+1)
=[(x2+1)2-x2 ](x4-x2+1)
=(x2+1-x)(x2+1 )(x4-x2+1)
a) a2 - b2 + 2a - 2b = (a + b)(a - b) + 2(a - b) = (a - b)(a + b + 2)
b) x2 + x - 12 = x2 + 4x - 3x - 12 = x(x + 4) - 3(x + 4) = (x - 3)(x + 4)
c) x4 + 4 = (x4 + 4x2 + 4) - 4x2 = (x2 + 2)2 - 4x2 = (x2 - 2x + 2)(x2 + 2x + 2)
Bài làm :
a) a2 - b2 + 2a - 2b = (a + b)(a - b) + 2(a - b) = (a - b)(a + b + 2)
b) x2 + x - 12 = x2 + 4x - 3x - 12 = x(x + 4) - 3(x + 4) = (x - 3)(x + 4)
c) x4 + 4 = (x4 + 4x2 + 4) - 4x2 = (x2 + 2)2 - 4x2 = (x2 - 2x + 2)(x2 + 2x + 2)
Chúc bạn học tốt !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!