\(\text{a},=49x^2+2.\left(-7x\right).9+81\\ b,=9y^2+2.\left(-3y\right).5x+25x^2\\ c,=9x^2+2.\left(-3x\right).\left(-7\right)+49\\ d,???\)

\(=\sqrt{6}-4\sqrt{6}+\dfrac{10\left(1+\sqrt{6}\right)}{1-6}-\sqrt{\left(\sqrt{6}-1\right)^2}=-3\sqrt{6}+\dfrac{10+10\sqrt{6}}{-5}-\sqrt{6}+1=-4\sqrt{6}-2-2\sqrt{6}+1=-6\sqrt{6}-1\)

\(\dfrac{x^2}{x-1}=\dfrac{7x+3}{8}\\ \dfrac{x^2.8-\left(7x+3\right)\left(x-1\right)}{8\left(x-1\right)}=0\\8 x^2-\left(7x^2+3x-7x-3\right)=0\\ 8x^2-7x^2+4x+3=0\\ x^2+4x+3=0\)

=>x= -1 , x=-3

Link : https://vi.wikipedia.org/wiki/Sigma

Mau chung : 8

\(\dfrac{3}{4}=\dfrac{3.2}{4.2}=\dfrac{6}{8};\dfrac{4}{8}\)

\(h,\left(-\dfrac{1}{5}\right).4\dfrac{1}{2}=\left(-\dfrac{1}{5}\right).\dfrac{9}{2}=-\dfrac{9}{10}\\ i,-3\dfrac{3}{4}:\left(-2,1\right)=-\dfrac{15}{4}.-\dfrac{10}{21}=\dfrac{63}{8}\)

Đang 1 lan th

a, \(=\dfrac{-1+-1.3}{21}=\dfrac{-4}{21}\\ b,=\dfrac{-5.12-1.9}{108}=\dfrac{-69}{108}=-\dfrac{23}{36}\\ c,=\dfrac{37}{5}-\left(-\dfrac{7}{5}\right)=\dfrac{44}{5}\\ d,=\dfrac{4.3-2}{3}=\dfrac{10}{3}\\ e,=-\dfrac{3}{7}+\left(\dfrac{10-4.7}{7}\right)=-\dfrac{3}{7}+-\dfrac{18}{7}=-3\\ f,=\dfrac{1}{15}-\dfrac{-1}{4}+\dfrac{14}{15}+\dfrac{3}{4}-\dfrac{3}{2}=\left(\dfrac{1}{15}+\dfrac{14}{15}\right)+\left(\dfrac{1}{4}+\dfrac{3}{4}\right)-\dfrac{3}{2}=1+1-\dfrac{3}{2}=\dfrac{1}{2}\\ g,-\dfrac{3}{2}.\left(-0,8\right)=-\dfrac{3}{2}.\left(-\dfrac{4}{5}\right)=\dfrac{6}{5}\)