myduyen9a

cau 1:a)ta giai ra duoc pt

$x^{2}-3x+2=0$ \Rightarrow x_{1}=1;x_{2}=2$

       b)$m< \frac{3}{2}$

$\sqrt{x+1}=t\geqslant 0\Rightarrow \sqrt{t^{2}-4t+4}+\sqrt{t^{2}-2t+1}=1 \Leftrightarrow \left | t-2 \right |+\left | t-1 \right |=1$

sau do ban xet dieu kien de tim duoc t

de cua ban khong duoc ro cho lam. nhung minh cung xin giai thu.

a)de roi chi can chung minh tong 2 goc doi =180 do la duoc.

$A^{2}=(\sqrt{a+b}+\sqrt{b+c}+\sqrt{c+a})^{2}\leq (1^{2}+1^{2}+1^{2}).(2a+2b+2c) \Rightarrow A^{2}\leq 6.(a+b+c)\Rightarrow A\leq \sqrt{6}$