\(\dfrac{2.3.5.\left(-7\right).12}{3.\left(-5\right).7.14}=\dfrac{2.3.5.\left(-7\right).12}{3.5.\left(-7\right).2.7}=\dfrac{12}{7}\)

\(\dfrac{2.3.5.\left(-7\right).12}{3.\left(-5\right).7.14}=\dfrac{1.1.1.\left(-1\right).12}{1.\left(-1\right).1.7}=\dfrac{-12}{-7}=\dfrac{12}{7}\)

a, 0

b,0

c, 0

mình ko chắc lắm

a/ (x+y)(x+y)

   =x+y.x+y

   =x+x.y+y

   =2.x.2.y

    =2.(x+y)

\(1.\\ A=\sqrt{\left(2+\sqrt{3}\right)^2}+\sqrt{\left(2-\sqrt{3}\right)^2}\\ =\left|2+\sqrt{3}\right|+\left|2-\sqrt{3}\right|\\ =2+\sqrt{3}+2-\sqrt{3}=4\)

\(2.\\a.\\ P=3x-\sqrt{\left(x-5\right)^2}=3x-\left|x-5\right|\\ b.\\ x=2\Rightarrow P=3\)

\(3.\\ M=\dfrac{\sqrt{\left(x-1\right)^2}}{x-1}=\dfrac{\left|x-1\right|}{x-1}\)

\(\cdot x>1\Rightarrow M=1\\ \cdot x=1\Rightarrow M=0\\\cdot x< 1\Rightarrow M=-1\)

B1.

Ta có:A\(=\sqrt{3+4\sqrt{3}+4}+\sqrt{3-4\sqrt{3}+4}\)

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

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

Bài 1 : 

\(A=\sqrt{\left(\sqrt{3}+2\right)^2}+\sqrt{\left(\sqrt{3}-2\right)^2}\\ =\sqrt{3}+2+2-\sqrt{3}=4\)

Bài 2 : 

a) \(P=3x-\sqrt{\left(x-5\right)^2}=3x-\left|x-5\right|\)

b) khi x = 2 thì \(P=3.2-\left|2-5\right|=3\)

Bài 3 : 

\(M=\dfrac{\sqrt{\left(\sqrt{x}-1\right)^2}}{x-1}=\dfrac{\left|\sqrt{x}-1\right|}{x-1}\)

\(A=\left(\frac{x+1}{x-1}-\frac{x-1}{x+1}\right):\frac{2x}{5.\left(x+1\right)}\)

\(A=\left(\frac{x^2+2x+1}{\left(x+1\right).\left(x-1\right)}-\frac{x^2-2x+1}{\left(x+1\right).\left(x-1\right)}\right):\frac{2x}{5.\left(x+1\right)}\)

\(A=\frac{x^2+2x+1-x+2x-1}{\left(x+1\right).\left(x-1\right)}\cdot\frac{5.\left(x+1\right)}{2x}\)

\(A=\frac{4x}{\left(x+1\right).\left(x-1\right)}\cdot\frac{5.\left(x+1\right)}{2x}=\frac{10}{x-1}\)

Cảm ơn bn nhiều!

bạn chi mình cách bấm phân số đi rồi mình làm cho

\(A=-5x^3y^2\)

a) \(A=\dfrac{1}{x+5}+\dfrac{2}{x-5}-\dfrac{2x+10}{\left(x+5\right)\left(x-5\right)}\)

\(A=\dfrac{x-5+2x+10-2x-10}{\left(x+5\right)\left(x-5\right)}=\dfrac{x-5}{\left(x+5\right)\left(x-5\right)}=\dfrac{1}{x+5}\)

b) \(A=-3\Rightarrow\dfrac{1}{x+5}=-3\)

\(\Leftrightarrow x+5=-\dfrac{1}{3}\Leftrightarrow x=-\dfrac{1}{3}-5=\dfrac{-16}{3}\)

\(9x^2-42x+49=\left(3x-7\right)^2=\left(3.\dfrac{-16}{3}-7\right)^2=\left(-23\right)^2=529\) \(\left(x=\dfrac{-16}{3}\right)\)

3x^n-2 ( xⁿ⁺² - yⁿ⁺² ) + yⁿ⁺² ( 3x^n-2 - y^n-2 )= 3x²ⁿ - 3x^n-2yⁿ⁺² + 3x^n-2yⁿ⁺² - y²ⁿ

                                                                 =3x²ⁿ - y²ⁿ

Mk nghĩ đáp án là vậy, nếu đúng thì k mk nha

CHÚC BẠN HỌC TỐT!!!!

\(3x^{n-2}.\left(x^{n-2}-y^{n+2}\right)+y^{n+2}\left(3x^{n-2}-y^{n-2}\right)\)

\(=3x^{2n}-3xy^{2n}+3xy^{2n}-y^{2n}\)

\(=3x^{2n}-y^{2n}\)