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\(2x^4-21x^3+74x^2-105x+50=0\)
\(< =>2x^4-10x^3-11x^3+55x^2+19x^2-95x^2-10x+50=0\)
\(< =>2x^3\left(x-5\right)-11x^2\left(x-5\right)+19x\left(x-5\right)-10\left(x-5\right)=0\)
\(< =>\left(x-5\right).\left(2x^3-11x^2+19x-10\right)=0\)
\(< =>\left(x-5\right).\left(2x^3-2x^2-9x^2+9x+10x-10\right)=0\)
\(< =>\left(x-5\right).\left(x-1\right).\left(2x^2-9x+10\right)=0\)
\(2x^2-9x+10\ge0\)
\(< =>x=5\)hoặc \(x=1\)
Vậy S = 1 hoặc 5
![](https://rs.olm.vn/images/avt/0.png?1311)
b: Xét tứ giác MAIO có
\(\widehat{OIM}=\widehat{OAM}=90^0\)
Do đó: MAIO là tứ giác nội tiếp
![](https://rs.olm.vn/images/avt/0.png?1311)
`a)M=(x+2)/(xsqrtx-1)+(sqrtx+1)/(x+sqrtx+1)-1/(sqrtx-1)(x>=0,x ne 1)`
`M=(x+2)/((sqrtx-1)(x+sqrtx+1))+((sqrtx+1)(sqrtx-1))/((sqrtx-1)(x+sqrtx+1))-(x+sqrtx+1)/((sqrtx-1)(x+sqrtx+1))`
`M=(x+2+x-1-x-sqrtx-1)/((sqrtx-1)(x+sqrtx+1))`
`M=(x-sqrtx)/((sqrtx-1)(x+sqrtx+1))`
`M=(sqrtx(sqrtx-1))/((sqrtx-1)(x+sqrtx+1))`
`M=sqrtx/(x+sqrtx+1)`
`b)x=25(tmđk)`
`=>sqrtx=5`
`=>M=5/(25+5+1)`
`=>M=5/31`
`c)M=sqrtx/(x+sqrtx+1)`
`x=0=>M=0<1/3`
`x>0=>M=1/(sqrtx+1+1/sqrtx)`
Áp dụng bđt cosi:
`sqrtx+1/sqrtx>=2`
`=>sqrtx+1+1/sqrtx>=3>0`
`=>M<=1/3`
Dấu "=" xảy ra khi `sqrtx=1/sqrtx<=>x=1`(KTMĐKXĐ)
`=>M<1/3`
Vậy `M<1/3`
`d)M=2/7`
`<=>sqrtx/(x+sqrtx+1)=2/7`
`<=>2x+2sqrtx+2=7`
`<=>2x-5sqrtx+2=0`
`<=>2x-4sqrtx-sqrtx+2=0`
`<=>(sqrtx-2)(2sqrtx-1)=0`
`<=>[(sqrtx=2),(2sqrtx=1):}`
`<=>[(x=4),(x=1/4):}(TMĐK)`
`e)` Vì `x>=0=>sqrtx>=0`
`=>x+sqrtx+1>=1>0`
`=>M>=0`
Mặt khác:`M<1/3`(câu b)
`=>M<1=>M-1<0`
`=>M(M-1)<=0`
`<=>M^2-M<=0`
`<=>M^2<=M`
a: Ta có: \(\dfrac{x+2}{x\sqrt{x}-1}+\dfrac{\sqrt{x}+1}{x+\sqrt{x}+1}-\dfrac{1}{\sqrt{x}-1}\)
\(=\dfrac{x+2+x-1-x-\sqrt{x}-1}{\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right)}\)
\(=\dfrac{x-\sqrt{x}}{\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right)}\)
\(=\dfrac{\sqrt{x}}{x+\sqrt{x}+1}\)
b: Thay x=25 vào M, ta được:
\(M=\dfrac{5}{25+5+1}=\dfrac{5}{31}\)
c: Ta có: \(M-\dfrac{1}{3}\)
\(=\dfrac{\sqrt{x}}{x+\sqrt{x}+1}-\dfrac{1}{3}\)
\(=\dfrac{3\sqrt{x}-x-\sqrt{x}-1}{3\left(x+\sqrt{x}+1\right)}\)
\(=\dfrac{-\left(x-2\sqrt{x}+1\right)}{3\left(x+\sqrt{x}+1\right)}\)
\(=\dfrac{-\left(\sqrt{x}-1\right)^2}{3\left(x+\sqrt{x}+1\right)}< 0\forall x\) thỏa mãn ĐKXĐ
hay \(M< \dfrac{1}{3}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a, sinC = \(\frac{AB}{BC}\); tanC = \(\frac{AB}{AC}\)
cosC = \(\frac{AC}{BC}\); cotC = \(\frac{AC}{AB}\)
b, Xét tam giác ABC vuông tại A, đường cao AH
tanB = \(\frac{AC}{AB}=\sqrt{2}\Rightarrow AC=\sqrt{2}AB\)
* Áp dụng hệ thức : \(\frac{1}{AH^2}=\frac{1}{AB^2}+\frac{1}{AC^2}\Rightarrow\frac{1}{12}=\frac{1}{AB^2}+\frac{1}{2AB^2}\Rightarrow AB\approx4,24\)cm
\(\Rightarrow AC\approx4,24\sqrt{2}\)cm
Theo định lí Pytago tam giác ABC vuông tại A
\(BC=\sqrt{AB^2+AC^2}\approx\sqrt{4,24^2+\left(4,24\sqrt{2}\right)^2}\approx7,34\)cm
Bài 1:
a: \(\sqrt{x-1}+2\sqrt{9x-9}-14=0\)
\(\Leftrightarrow7\sqrt{x-1}=14\)
\(\Leftrightarrow x-1=4\)
hay x=5