\(=\left(2\sqrt{2}+5\sqrt{2}\right).\sqrt{2}\)

\(=7\sqrt{2}.\sqrt{2}\)

\(=14\)

\(M=\dfrac{x+3+2\left(\sqrt{x}-3\right)-\left(\sqrt{x}+3\right)}{\left(\sqrt{x}+3\right)\left(\sqrt{x}-3\right)}\)

\(M=\dfrac{x+3+2\sqrt{x}-6-\sqrt{x}-3}{\left(\sqrt{x}+3\right)\left(\sqrt{x}-3\right)}\)

\(M=\dfrac{x+\sqrt{x}-6}{\left(\sqrt{x}+3\right)\left(\sqrt{x}-3\right)}\)

\(M=\dfrac{\left(\sqrt{x}+3\right)\left(\sqrt{x}-2\right)}{\left(\sqrt{x}+3\right)\left(\sqrt{x}-3\right)}\)

\(M=\dfrac{\sqrt{x}-2}{\sqrt{x}-3}\)

c)\(64x^2-48x+9-\left(64x^2+144x+81\right)=12\)

\(64x^2-48x-3-64x^2-144x-81=0\)

\(-192x=84\)

\(x=-\dfrac{7}{16}\)

a) \(36x^2-1-\left(36x^2-36x+9\right)=8\)

\(36x^2-1-36x^2+36x-9-8=0\)

\(36x=18\)

\(x=\dfrac{1}{2}\)

\(\dfrac{1}{2}-\left|x-3\right|=2\)

\(\left|x-3\right|=-\dfrac{3}{2}\)

\(\rightarrow\)không tìm được x thỏa mãn 

a) \(=x^2+7x-12x-84-2x+14\)

\(=x^2-7x-70\)

b)\(=x^2-4x-2x+8\)

\(=x\left(x-4\right)-2\left(x-4\right)\)

 \(=\left(x-4\right)\left(x-2\right)\)

c) \(=9x\left(x+y\right)-\left(x+y\right)\)

\(=\left(9x-1\right)\left(x+y\right)\)

d)\(=\left(x-y\right)^2-9^2\)

\(=\left(x-y+9\right)\left(x-y-9\right)\)

e)\(=x^2+8x+16-60+15x\)

\(=x^2+23x-44\)

a) Áp dụng định lí Pytago trong \(\Delta\) AHC vuông tại H ta có :

      \(AH^2+HC^2=AC^2\)

\(\Rightarrow HC^2=AC^2-AH^2\)

\(\Rightarrow HC=\sqrt{AC^2-AH^2}=\sqrt{40^2-24^2}=32cm\)

b)  Áp dụng định lí Pytago trong \(\Delta\) AHC vuông tại H ta có :

      \(AH^2+HC^2=AC^2\)

\(\Rightarrow AC=\sqrt{AH^2+HC^2}=\sqrt{9,6^2+12,8^2}=16cm\)

\(-\dfrac{1}{4}.\dfrac{4}{17}.\dfrac{-68}{21}.\dfrac{-7}{23}\)

=\(\dfrac{-1}{17}.\dfrac{68}{69}\)

=\(\dfrac{-4}{69}\)

a) X hóa trị III

b) \(X_2\left(SO_4\right)_3\) 

\(\Rightarrow\sqrt{\left(x-3\right)^2}=5^2\)

\(\Rightarrow\left|x-3\right|=5\)

\(\Rightarrow x-3=5\)          hoặc   \(x-3=-5\)

\(\Rightarrow x=8\)                           \(\Rightarrow x=-2\)