=>\(\sqrt{5x+1}\left(\sqrt{5}-6\sqrt{5}-\dfrac{1}{4}\right)=\dfrac{27\sqrt{5}}{4}\)

=>căn 5x+1=\(\dfrac{27\sqrt{5}}{28\sqrt{5}-1}\)

=>5x+1=0,96

=>5x=-0,04

=>x=-0,04/5=-0,008

a: \(=3\sqrt{5}+2\sqrt{5}-2\sqrt{5}=3\sqrt{5}\)

b: \(=2\sqrt{2}+2\sqrt{2}+5\sqrt{2}=9\sqrt{2}\)

c: \(=4\sqrt{3}+3\sqrt{3}-3\sqrt{5}+2\sqrt{5}=7\sqrt{3}-\sqrt{5}\)

d: \(=5\sqrt{3}+4\sqrt{3}-10\sqrt{3}=-\sqrt{3}\)

e: \(=\left(\sqrt{7}-2\sqrt{3}\right)\cdot\sqrt{7}+2\sqrt{21}\)

=7-2*căn 21+2*căn 21

=7

f: \(=\left(2\sqrt{11}-3\sqrt{2}\right)\cdot\sqrt{11}+3\sqrt{22}\)

=22-3*căn 22+3*căn 22

=22

a) \(3\sqrt{5}+\sqrt{20}-2\sqrt{5}\)

\(=3\sqrt{5}+2\sqrt{5}-2\sqrt{5}\)

\(=3\sqrt{5}\)

b) \(2\sqrt{2}+\sqrt{8}+\sqrt{50}\)

\(=2\sqrt{2}+2\sqrt{2}+5\sqrt{2}\)

\(=9\sqrt{5}\)

c) \(4\sqrt{3}+\sqrt{27}-\sqrt{45}+2\sqrt{5}\)

\(=4\sqrt{3}+3\sqrt{3}-3\sqrt{5}+2\sqrt{5}\)

\(=7\sqrt{3}-\sqrt{5}\)

d) \(\sqrt{75}+\sqrt{48}-\sqrt{300}\)

\(=5\sqrt{3}+4\sqrt{3}-10\sqrt{3}\)

\(=-\sqrt{3}\)

e) \(\left(\sqrt{28}-\sqrt{12}-\sqrt{7}\right)\sqrt{7}+2\sqrt{21}\)

\(=\left(2\sqrt{7}-2\sqrt{3}-\sqrt{7}\right)\sqrt{7}+2\sqrt{21}\)

\(=\left(\sqrt{7}-2\sqrt{3}\right)\sqrt{7}+2\sqrt{21}\)

\(=7-2\sqrt{21}+2\sqrt{21}\)

\(=7\)

f) \(\left(\sqrt{99}-\sqrt{18}-\sqrt{11}\right)\sqrt{11}+3\sqrt{22}\)

\(=\left(3\sqrt{11}-3\sqrt{2}-\sqrt{11}\right)\sqrt{11}+3\sqrt{22}\)

\(=\left(2\sqrt{11}-3\sqrt{2}\right)\sqrt{11}+3\sqrt{22}\)

\(=22-3\sqrt{22}+3\sqrt{22}\)

\(=22\)

g) \(3\sqrt{45}-5\sqrt{125x}+7\sqrt{20x}+28\)

\(=9\sqrt{5}-25\sqrt{5x}+14\sqrt{5x}+28\)

\(=9\sqrt{5}-11\sqrt{5x}+28\)

a: \(\Leftrightarrow\left(x+12-3x\right)\left(x+12+3x\right)=0\)

=>(-2x+12)(4x+12)=0

=>x=-3 hoặc x=6

b: \(\Leftrightarrow20x^3-15x^2+45x-45=0\)

=>\(x\simeq0.93\)

d: =>-4x+28+11x=-x+3x+15

=>7x+28=2x+15

=>5x=-13

=>x=-13/5

e: \(\Leftrightarrow4x^3-12x+x=4x^3-3x+5\)

=>-9x=-3x+5

=>-6x=5

=>x=-5/6

\(\dfrac{20x^{2}-45}{4x^{2}+12x+9}\)\(=\dfrac{5.(4x^{2}-9)}{(2x)^{2}+2.2x.3+3^{2}}\)\(=\dfrac{5(2x-3)(2x+3)}{(2x+3)^{2}}\)\(=\dfrac{5(2x-3)}{2x+3}\)

9x² +12x -45 = (3x)²  + 2 . 3x . 2 + 4 - 49

= ( (3x)² + 2 . 3x . 2 + 2² ) - 49 

= ( 3x + 2 )² - 7² 

= ( 3x + 2 - 7 )( 3x + 2 - 7 )

\( \dfrac{7}{8}x - 5x + 45 = \dfrac{{20x + 1,5}}{6}\\ \Leftrightarrow \dfrac{7}{8}x - 5\left( {x - 9} \right) = \dfrac{{20x + 1,5}}{6}\\ \Leftrightarrow 42x - 240x + 2160 = 160x + 12\\ \Leftrightarrow - 358x = - 2148\\ \Leftrightarrow x = 6 \)

\(\frac{7}{8}x-5x+45=\frac{20x+1,5}{6}\)

\(\Leftrightarrow\frac{7x}{8}-\frac{5x+45}{1}=\frac{20x+1,5}{6}\)

\(\Leftrightarrow\frac{7x.3}{8.3}-\frac{24.\left(5x+45\right)}{24}=\frac{4.\left(20x+1,5\right)}{6.4}\)

\(\Leftrightarrow\frac{21x}{24}-\frac{24.\left(5x+45\right)}{24}=\frac{4.\left(20x+1,5\right)}{24}\)

\(\Rightarrow21x-24.\left(5x+45\right)=4.\left(20x+1,5\right)\)

\(\Leftrightarrow21x-120x-1080=80x+6\)

\(\Leftrightarrow-99x-1080=80x+6\)

\(\Leftrightarrow-99x-80x=6+1080\)

\(\Leftrightarrow-179x=1086\)

\(\Leftrightarrow x=1086:\left(-179\right)\)

\(\Leftrightarrow x=-\frac{1086}{179}\)

Vậy phương trình có tập hợp nghiệm là: \(S=\left\{-\frac{1086}{179}\right\}.\)

Chúc bạn học tốt!

\( \dfrac{7}{8}x - 5x + 45 = \dfrac{{20x + 1,5}}{6}\\ \Leftrightarrow \dfrac{7}{8}x - 5\left( {x - 9} \right) = \dfrac{{20x + 1,5}}{6}\\ \Leftrightarrow 21x - 120x + 1080 = 80x + 6\\ \Leftrightarrow - 179x = - 1074\\ \Leftrightarrow x = 6 \)

Ta có \(x=21\Rightarrow x-1=20\)

biểu thức B có dạng :

 \(B=x^6-\left(x-1\right)x^5-\left(x-1\right)x^4-\left(x-1\right)x^3-\left(x-1\right)x^2-\left(x-1\right)x+3\)

\(=x^6-x^6+x^5-x^5+x^4-x^4+x^3-x^3+x^2-x^2+x+3=x+3\)

Vậy \(B=21+3=24\)

\(M=x^6-20x^5-20x^4-20x^3-20x^2-20x+3\)

\(M=x^6-\left(x-1\right)x^5-\left(x-1\right)x^4-\left(x-1\right)x^3-\left(x-1\right)x^2-\left(x-1\right)x+3\)

\(M=x^6-x^6+x^5-x^5+x^4-x^4+x^3-x^3+x^2-x+3\)

\(M=x+3\) (1)

Thay \(x=21\)vào (1) ta được:

\(M=21+3\)

\(M=24\)

Còn câu N bạn tham khảo tại link này nha:

Câu hỏi của Hoang Linh - Toán lớp 8 | Học trực tuyến

Chúc bạn học thật tốt!