bạn viết thế này khó nhìn quá

nhìn hơi đau mắt nhá bạn hoa mắt quá

1:

\(A=\sqrt{x^2+\dfrac{2x^2}{3}}=\sqrt{\dfrac{5x^2}{3}}=\left|\sqrt{\dfrac{5}{3}}x\right|=-x\sqrt{\dfrac{5}{3}}\)

2: \(=\left(\dfrac{\sqrt{100}+\sqrt{40}}{\sqrt{5}+\sqrt{2}}+\sqrt{6}\right)\cdot\dfrac{2\sqrt{5}-\sqrt{6}}{2}\)

\(=\dfrac{\left(2\sqrt{5}+\sqrt{6}\right)\left(2\sqrt{5}-\sqrt{6}\right)}{2}\)

\(=\dfrac{20-6}{2}=7\)

dễ mà bạn, cái này thì phải tự làm thôi!

1:

I2x+3I = 5

=> 2x+3 = 5 hoặc 2x+3 = -5

=> 2x = 5 - 3 hoặc 2x = -5 - 3

=> 2x = 2 hoặc 2x = -8

=> x = 2 hoặc x = -4

2:

B = 1/2.2/3.3/4.4/5.....27/28

   = 1.2.3.4.5.6...27/2.3.4.5.6...28

   = 1/28                                                                                                                          

3:

2A = 2(1+1/2+1/2^2+1/2^3+1/2^4+...+1/2^2015) = 2+1+1/2+1/2^2+1/2^3+...+1/2^2014

=> 2A-A = ( 2+1+1/2+1/2^2+1/2^3+...+1/2^2014)-(1+1/2+1/2^2+1/2^3+...+1/2^2015)

=> A = 2-1/2^2015

\(a,C=\dfrac{2x^2-x-x-1+2-x^2}{x-1}\left(x\ne1\right)\\ C=\dfrac{x^2-2x+1}{x-1}=\dfrac{\left(x-1\right)^2}{x-1}=x-1\\ b,D=\dfrac{1+\sqrt{a}}{\sqrt{a}\left(\sqrt{a}-1\right)}\cdot\dfrac{\left(\sqrt{a}-1\right)^2}{\sqrt{a}+1}\left(a>0;a\ne1\right)\\ D=\dfrac{\sqrt{a}-1}{\sqrt{a}}\)

Có 

\(=x^2-2x+1+x^2+6x+9-2x^2+10x=14x+10\)

Câu 4: 

\(=\dfrac{a\left(a-b\right)-c\left(a-b\right)}{a\left(a+b\right)-c\left(a+b\right)}=\dfrac{a-b}{a+b}\)

A. ( x -5 ) ( 7x + 1 ) - 7x ( x + 3)

= 7x² + x - 35x - 5 - 7x² - 21x

= (7x²-7x²) + (x - 35x - 21x) -5

= -56x - 5

B = (x² - 2x.2 + 2²) - x² + 1²

B = (x² - x²) - 4x + (2 + 1)

B= -4x +3

A. (x - 5)(7x + 1) - 7x(x + 3)

= 7x² + x - 35x - 5 - 7x² - 21x

= (7x² - 7x²) + (x - 35x - 21x) - 5

= -55x - 5

B. (x - 2)² - (x - 1)(x + 1)

= x² - 4x + 4 - x² + 1

= (x² - x²) - 4x + (4 + 1)

= -4x + 5

\(A=(xy^2-1)(x^2y+5)-xy^2(x^2y+5)\\=(x^2y+5)(xy^2-1-xy^2)\\=(x^2y+5)\cdot(-1)\\=-x^2y-5\)

A=( xy^2-1)(x^2y+5)-xy^2( x^2y+5)

=xy^2.(x^2y+5)-1.(x^2y+5)-x^3y^3-5xy^2

=-x^2-5 ( bước này làm tắc )

A = -(x + 2)(x - 5) + (x - 1)(x - 2)

A = -x² + 3x + 10 + x² - 3x + 2

A = (-x² + x²) + (3x - 3x) + 10 + 2

A = 12

\(\left(x-1\right)^3-x\left(x-2\right)\left(x+2\right)+3\left(x-5\right)^2\\ =x^3-3x^2+3x-1-x\left(x^2-4\right)+3\left(x^2-10x+25\right)\)

\(=x^3-3x^2+3x-1-x^3+4x+3x^2-30x+75\)

\(=74-23x\)