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a)x7+x5+1=x7+x6-x6+2x5-x5+x4-x4+x3-x3+x2-x2+1
=x7-x6+x5-x3+x2+x6-x5+x4-x2+x+x5-x4+x3-x+1
=x2(x5-x4+x3-x+1)+x(x5-x4+x3-x+1)+1(x5-x4+x3-x+1)
=(x2+x+1)(x5-x4+x3-x+1)
b)4x4-32x2+1=4x4+12x3+2x2-12x3-36x2-6x+2x2+6x+1
=2x2(2x2+6x+1)-6x(2x2+6x+1)+1(2x2+6x+1)
=(2x2-6x+1)(2x2+6x+1)
c)x6+27=(x2+3)(x2-3x+3)(x2+3x+3)
d)3(x4+x2+1)-(x2+x+1)
=3x4-3x3+2x2+3x3-3x2+2x+3x2-3x+2
=x2(3x2-3x+2)+x(3x2-3x+2)+1(3x2-3x+2)
=(x2+x+1)(3x2-3x+2)
e)bạn tự làm nhé
a, \(x.\sqrt{\frac{2}{5}}\) = \(\sqrt{x^2}.\sqrt{\frac{2}{5}}\) = \(\sqrt{\frac{x^2.2}{5}}\)
b, \(\left(x-5\right).\sqrt{\frac{x}{25-x^2}}\)= \(\sqrt{\left(x-5\right)^2}\). \(\sqrt{\frac{x}{\left(5-x\right)\left(5+x\right)}}\) = \(\sqrt{\frac{\left(x-5\right)^2.x}{\left(x-5\right)\left(x+5\right)}}\)= \(\sqrt{\frac{x.\left(x-5\right)}{x+5}}\)
c,\(x.\sqrt{\frac{7}{x^2}}\) = \(\sqrt{x^2}\). \(\sqrt{\frac{7}{x^2}}\) = \(\sqrt{\frac{x^2.7}{x^2}}\) = \(\sqrt{7}\)