Xét △ABC có: A + B + C = 180^o  

=> A + 70^o + 40^o = 180^o  

=> A =   70^o  

Vì AD là phân giác của A

=> BAD = DAC = A/2 = 70^o / 2 = 35^o  

Xét △ABC có: DAC + C + ADC = 180^o 

=> 35^o + 40^o + ADC = 180^o 

=> ADC = 105^o 

Ta có: ADC + ADB = 180^o (2 góc kề bù) 

=> 105^o + ADB = 180^o 

=> ADB = 75^o 

có hình ko bạn

\(\left(2\sqrt{3}\right)^2-\left(3\sqrt{2}\right)^2+\left(4\sqrt{0,5}\right)^2-\left(\frac{1}{5}\sqrt{125}\right)^2\)

\(=2^2.3-3^2.2+4^2.0,5-5\)

\(=12-18+8-5\)

\(=-3\)

                                                           Bài giải

\(\left(2\sqrt{3}\right)^2-\left(3\sqrt{2}\right)^2+\left(4\sqrt{0,5}\right)^2-\left(\frac{1}{5}\sqrt{125}\right)^2\)

\(=2^2\cdot3-3^2\cdot2+4^2\cdot0,5-\frac{1}{25}\cdot125\)

\(=12-18+8-5\)

\(=-3\)

a) \(x-2\sqrt{x}=0\)

\(\Rightarrow x=2\sqrt{x}\)\(\Rightarrow x^2=4x\)\(\Rightarrow x\left(x-4\right)=0\)

\(\Rightarrow x=0\)hoặc \(x=4\)

Vậy \(x=0\)hoặc \(x=4\)

b) \(x=\sqrt{x}\)\(\Rightarrow x^2=x\)\(\Rightarrow x\left(x-1\right)=0\)

\(\Rightarrow\)\(x=0\)hoặc \(x=1\)

Vậy \(x=0\)hoặc \(x=1\)

\(b,\text{ }x=\sqrt{x}\)

\(x^2=x\)

\(x^2-x=0\)

\(x\left(x-1\right)=0\)

\(\Rightarrow\orbr{\begin{cases}x=0\\x-1=0\end{cases}}\)                \(\Rightarrow\orbr{\begin{cases}x=0\\x=0+1\end{cases}}\)             \(\Rightarrow\orbr{\begin{cases}x=0\\x=1\end{cases}}\)

\(\Rightarrow\text{ }x\in\left\{0\text{ ; }1\right\}\)

ta có \(A=\frac{2^6+3.2^4+2^7}{2^5}=\frac{2^4\left(2^2+3+2^3\right)}{2^5}=\frac{4+3+8}{2}=\frac{15}{2}\)

Ta có:

B = \(\frac{2a+9}{a+3}-\frac{5a+17}{a+3}-\frac{3a}{a+3}\)

B = \(\frac{\left(2a+9\right)-\left(5a+17\right)-3a}{a+3}\)

B = \(\frac{2a+9-5a-17-3a}{a+3}\)

B = \(\frac{-6a-8}{a+3}=\frac{-6\left(a+3\right)+10}{a+3}=-6+\frac{10}{a+3}\)

Để B \(\in\)Z <=> 10 \(⋮\)a + 3  <=> a + 3 \(\in\)Ư(10) = {1; -1; 2; -2; 5; -5; 10; -10}

Lập bảng : 

Vậy ...

\(B=\frac{2a+9}{a+3}-\frac{5a+17}{a+3}-\frac{3a}{a+3}\)

\(B=\frac{2a+9-5a-17-3a}{a+3}\)

\(B=\frac{-6a-8}{a+3}\inℤ\)

\(\Leftrightarrow-6a-8⋮a+3\)

\(\Rightarrow-6a-18+10⋮a+3\)

\(\Rightarrow-6\left(a+3\right)+10⋮a+3\)

\(\Rightarrow10⋮a+3\)

\(\Rightarrow a+3\in\left\{-1;1;-2;2;-5;5;-10;10\right\}\)

\(\Rightarrow a\in\left\{-4;-2;-5;-1;-8;2;-13;7\right\}\)

Có C = 1,5 - |x + 1,1|=-|x+1,1|+1,5

Vì |x+1,1|>=0

=) -|x+1,1|<=0

=) C = 1,5 - |x + 1,1| <=1,5

Dấu '=' xay ra khi

x+1,1=0

x=-1,1