\(W_đ=\dfrac{1}{2}mv^2=\dfrac{1}{2}.m.2as=\dfrac{1}{2}.2.2.10.100=2kJ\)

#397 chị đayyyy e:D

#408 Lâm nà: https://m.facebook.com/profile.php?id=100073660307540

\(=\dfrac{\sqrt{a}+1}{\left(\sqrt{a}-2\right)\left(\sqrt{a}+2\right)}-\dfrac{\sqrt{a}-1}{\left(\sqrt{a}+2\right)^2}\left(\dfrac{\sqrt{a}\left(a+2\sqrt{a}-4\right)-2}{\sqrt{a}}\right)\\ =\dfrac{\left(\sqrt{a}+1\right)\left(\sqrt{a}+2\right)-\left[\left(\sqrt{a}-1\right)\left(\sqrt{a}-2\right)\right]}{\left(\sqrt{a}+2\right)^2\left(\sqrt{a}-2\right)}.\left(a+2\sqrt{a}+1-5\right)-2\\ =\dfrac{a+3\sqrt{a}+2-a+3\sqrt{a}+2}{\left(\sqrt{a}+2\right)^2\left(\sqrt{a}-2\right)}\left(\sqrt{a}+2\right)^2-7\)   

\(=\dfrac{6\sqrt{a}+4}{\sqrt{a}-2}-7=\dfrac{6\sqrt{a}+4-7\sqrt{a}+14}{\sqrt{a}-2}\\ =\dfrac{-\sqrt{a}+18}{\sqrt{a}-2}\)

16, Có \(cosa>0\Rightarrow0< a< 90\) 

\(cosa=\dfrac{1}{3}\Rightarrow a\approx649,5\Rightarrow sin\left(649,5\right)\approx\dfrac{-2\sqrt{2}}{3}\) 

17, \(cosa< 0\Rightarrow90^o< a< 180\\ sin\left(135\right)=sin\left(180-135\right)=sin45=\dfrac{\sqrt{2}}{2}\) 

\(\Leftrightarrow sin\left(45\right)< sina\Leftrightarrow sin\left(135\right)< sina\Rightarrow D\) 

18, \(c^2=a^2+b^2-2abcosC\\ \Rightarrow c=\sqrt{\sqrt{2}^2+\sqrt{3}^2-2.\sqrt{2}\sqrt{3}cos30}=\left(C\right)\) 

\(19,2bccosA=b^2+c^2-a^2\\ \Rightarrow cosA=\dfrac{5^2+8^2-7^2}{2.5.8}=\dfrac{1}{2}\Rightarrow A=60^o\)  

\(20,B=180-30-75=75^o\\ \dfrac{b}{sinB}=\dfrac{c}{sinC}\Leftrightarrow\dfrac{4}{sin\left(75\right)}=\dfrac{c}{sin75}\Rightarrow c=AB=4\\ \Rightarrow S_{ABC}=\dfrac{1}{2}bcsinA=8\\ 21,\dfrac{8\left(c\right)}{sinC}=\dfrac{4\sqrt{6}}{sin60}\Rightarrow C=45^o\\ 22,cos\left(A+B\right)=\dfrac{-1}{5}\Rightarrow\left(a+b\right)\approx101^o\Rightarrow C=79^o\\ c^2=a^2+b^2-2abcosC\Rightarrow c\approx7\)

\(11,B.\left(A\cap B\right)\mathbb{C}\\ 12,x=0\Rightarrow y=2\\ y=0\Rightarrow x=2\Rightarrow\left(B\right)\) 

(loại Đáp Án A với B vì thay 0 vào bpt có \(0+0\ge2\) (sai => gạch O )

\(13,C\) 

\(14,\) Thay số lần lượt vào các pt \(\Rightarrow D\) 

kudo shinichi nx nha đậu chuyên đó:) tên fb là j k nhớ:D

Vì nó là phần bù nên phải đổi ngoặc:)?