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\(\sqrt{x^3}-1=\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right).\)
x8 + x + 1
= (x8 + x7 + x6) + (- x7 - x6 - x5) + (x5 + x4 + x3) + (- x4 - x3 - x2) + (x2 + x + 1)
= (x2 + x + 1)(x6 - x5 + x3 - x2 + 1)
Ta có: \(P\left(x\right)=x^4+6x^3+7x^2-6x+1\)
\(=x^4+\left(6x^3-2x^2\right)+\left(9x^2-6x+1\right)\)
\(=x^4+2x^2\left(3x-1\right)+\left(3x-1\right)^2\)
\(=\left(x^2+3x-1\right)^2\)
\(C=x^2\left(x^2+x+1\right)-2x\left(x^2+x+1\right)+3\left(x^2+x+1\right)\)
\(=\left(x^2+x+1\right)\left(x^2-2x+3\right)\)
xét \(x\ne0\)ta có :
\(M=\)\(^{x^2\cdot\left(x^2+6x+7-\frac{6}{x}+\frac{1}{x^2}\right)}\)
Đặt \(x-\frac{1}{x}=t\Rightarrow t^2=x^2-2+\frac{1}{x^2}\Leftrightarrow t^2+2=x^2+\frac{1}{x^2}\)
Do đó \(M=x^2\cdot\left(t^2+2+6t+7\right)\Leftrightarrow x^2\cdot\left(t^2+6t+9\right)\)
\(\Leftrightarrow M=x^2\cdot\left(t+3\right)^2\)
M=\(x^4+3x^3-x^2+3x^3+9x^2-3x-x^2-3x+1\)
\(=x^2(x^2+3x-1)+3x\left(x^2+3x-1\right)-\left(x^2+3x-1\right)\)
\(=\left(x^2+3x-1\right)^2\)
\(M=7\sqrt{x-1}-\sqrt{x^2\left(x-1\right)}+\left(\sqrt{x-1}\right)^2=\sqrt{x-1}\left(7-x+\sqrt{x-1}\right)\)
\(=\sqrt{x-1}\left(6-\left(x-1\right)+\sqrt{x-1}\right)\)( đến đây bạn có thể đặt \(\sqrt{x-1}=t\),t>=0 rồi giải)
\(=-\sqrt{x-1}\left(\sqrt{x-1}-3\right)\left(\sqrt{x-1}+2\right)\)
\(8-\frac{x\sqrt{x}}{3}\)
\(=8-\frac{\sqrt{x^3}}{3}\)
\(=8-\frac{\left(\sqrt{x}\right)^3}{3}\)
\(=8-\frac{\left(\sqrt{x}\right)^3}{\left(\sqrt[3]{3}\right)^3}\)
\(=2^3-\left(\frac{\sqrt{x}}{\sqrt[3]{3}}\right)^3\)
\(=\left(2-\frac{\sqrt{x}}{\sqrt[3]{3}}\right)\left(4+\frac{2\sqrt{x}}{\sqrt[3]{3}}+\frac{x}{\left(\sqrt[3]{3}\right)^2}\right)\)
Bài làm:
Ta có: \(-6x+5\sqrt{x}+1\)
\(=\left(-6x+6\sqrt{x}\right)-\left(\sqrt{x}-1\right)\)
\(=-6\sqrt{x}\left(\sqrt{x}-1\right)-\left(\sqrt{x}-1\right)\)
\(=\left(-6\sqrt{x}-1\right)\left(\sqrt{x}-1\right)\)
\(=\left(6\sqrt{x}+1\right)\left(1-\sqrt{x}\right)\)
ko thể phân tích : biểu thức bất khả quy ^^