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a) 7x3 - 5x2
= x2( 7x - 5 )
b) x2 - 10x + 25
= x2 - 2.5.x + 52
= ( x - 5 )2
Ta có:\(7x^3-5x^2=x^2\left(7x-5\right)\)
\(x^2-10x+25=\left(x-5\right)^2\)
a, \(\left(4x+5\right)^2=\left(4x+5\right)\left(4x+5\right)=\left[\left(4x+5\right)4x\right]+\left[\left(4x+5\right)5\right]=4x^2+20x+25\)
b, \(\left(5x-2\right)^2=\left(5x-2\right)\left(5x-2\right)=\left[\left(5x-2\right)5x-\left(5x-2\right)2\right]=5x^2-10x+25\)
b, \(8^2-12x^2=\left(8^2-12x^2\right)\left(8^2+12x^2\right)\)
đúng ko :)
@No name: Bị sai rồi nhé, a,b,c sai hết :>
a) ( 4x + 5 )2
= ( 4x )2 + 2.4x.5 + 52
= 16x2 + 40x + 25
b) ( 5x - 2 )2
= ( 5x )2 - 2.5x.2 + 22
= 25x2 - 20x + 4
c) 82 - 12x2
= 64 - 12x2
= ( V8 - V12x )( V8 + V12x )
\(x^4-5x^2+4=x^4-x^2-4x^2+4=x^2\left(x^2-1\right)-4\left(x^2-1\right)=\left(x^2-4\right)\left(x^2-1\right)\)
\(=\left(x-2\right)\left(x+2\right)\left(x-1\right)\left(x+1\right)=\left(x-2\right)\left(x-1\right)\left(x+1\right)\left(x+2\right)\)
Ta có : x4 - 5x2 + 4
= x4 - x2 - 4x2 + 4
= x2(x2 - 1) + (4x2 - 4)
= x2(x2 - 1) + 4(x2 - 1)
= (x2 - 1)(x2 + 4)
\(x^4-3x^3+5x^2-9x+6\)
\(=x^4-2x^3-x^3+2x^2+3x^2-6x-3x+6\)
\(=x^3\left(x-2\right)-x^2\left(x-2\right)+3x\left(x-2\right)-3\left(x-2\right)\)
\(=\left(x-2\right)\left(x^3-x^2+3x-3\right)\)
\(=\left(x-2\right)\left[x^2\left(x-1\right)+3\left(x-1\right)\right]\)
\(=\left(x-2\right)\left(x-1\right)\left(x^2+3\right)\)
ta co: x^3 + 5x -6=x^3-x+6x-6=x.(x^2 - 1) + 6.(x-1) = x.(x-1).(x+1) + 6.(x-1) =(x-1).(x^2+x+6)