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a) \(BC^2=AB^2+AC^2\Rightarrow BC=\sqrt{AB^2+AC^2}=\sqrt{3^2+4^2}=5\left(cm\right)\)
\(\left\{{}\begin{matrix}sinB=\dfrac{AC}{BC}=\dfrac{4}{5}\Rightarrow\widehat{B}\approx53^0\\sinC=\dfrac{AB}{BC}=\dfrac{3}{5}\Rightarrow\widehat{C}=37^0\end{matrix}\right.\)
c) Ta có: \(\left\{{}\begin{matrix}AB=BD\\AC=DC\end{matrix}\right.\)(t/c 2 tiếp tuyến cắt nhau)
=> BC là đường trung trực AD
\(\Rightarrow AD\perp BC\)
Áp dụng HTL trong tam giác BDC vuông tại D:
\(FB.FC=FD^2\Rightarrow4FB.FC=4FD^2=\left(2FD\right)^2=AD^2\)
cái này áp dụng hệ thức lượng thôi bạn
AH=căn 6^2-4,8^2=3,6cm
=>AC=6^2/3,6=10cm
\(A=\dfrac{\left(\sqrt{x}+1\right)\left(x-\sqrt{x}+1\right)}{x-\sqrt{x}+1}-\dfrac{\left(\sqrt{x}-2\right)\left(\sqrt{x}+2\right)}{\sqrt{x}+2}\\ A=\sqrt{x}+1-\sqrt{x}+2=3\)
Anh có thể giải từng bước giúp e ko ạ e ch hỉu lắm í ạ em cảm ơn
\(n=\sqrt{2}\left(\sqrt{3}+1\right)\sqrt{2-\sqrt{3}}\\ n=\left(\sqrt{3}+1\right)\sqrt{4-2\sqrt{3}}\\ n=\left(\sqrt{3}+1\right)\sqrt{\left(\sqrt{3}-1\right)^2}\\ n=\left(\sqrt{3}+1\right)\left|\sqrt{3}-1\right|\\ n=\left(\sqrt{3}+1\right)\left(\sqrt{3}-1\right)\\ n=3-1=2\)
a: \(P=\left(\dfrac{2}{\sqrt{x}-1}+\dfrac{\sqrt{x}}{\sqrt{x}+1}\right)\cdot\dfrac{\sqrt{x}}{x+\sqrt{x}+2}\)
\(=\dfrac{2\sqrt{x}+2+x-\sqrt{x}}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}\cdot\dfrac{\sqrt{x}}{x+\sqrt{x}+2}\)
\(=\dfrac{\sqrt{x}}{x-1}\)
\(P=\left(\dfrac{2}{\sqrt{x}-1}+\dfrac{\sqrt{x}}{\sqrt{x}+1}\right).\dfrac{\sqrt{x}}{x+\sqrt{x}+2}\)
\(\Rightarrow P=\dfrac{2\left(\sqrt{x}+1\right)+\sqrt{x}\left(\sqrt{x}-1\right)}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}.\dfrac{\sqrt{x}}{x+\sqrt{x}+2}\)
\(\Rightarrow P=\dfrac{x+\sqrt{x}+2}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}.\dfrac{\sqrt{x}}{x+\sqrt{x}+2}\)
\(\Rightarrow P=\dfrac{\sqrt{x}}{x-1}\)
\(\Rightarrow P=\dfrac{\sqrt{3+2\sqrt{2}}}{3+2\sqrt{2}-1}\)
\(\Rightarrow P=\dfrac{\sqrt{\left(\sqrt{2}+1\right)^2}}{2+2\sqrt{2}}\)
\(\Rightarrow P=\dfrac{\sqrt{2}+1}{2\left(\sqrt{2}+1\right)}\)
\(\Rightarrow P=\dfrac{1}{2}\)
\(26,\\ a,\sin45^0=\cos45^0< \sin50^025'< \sin57^048'=\cos32^012'< \sin72^0=\cos18^0< \sin75^0\\ b,\tan37^026'< \tan47^0< \tan58^0=\cot32^0< \tan63^0< \tan66^019'=\cot23^041'\\ 27,\\ A=\dfrac{\left(\sin^226^0+\sin^264^0\right)+2\left(\cos^215^0+\cos^275^0\right)}{\left(\sin^255^0+\cos^255^0\right)+\left(\sin^242^0+\cos^242^0\right)}-\dfrac{\tan81^0}{2\tan81^0}\\ A=\dfrac{\left(\sin^226^0+\cos^226^0\right)+2\left(\sin^215^0+\cos^215^0\right)}{1+1}-\dfrac{1}{2}\\ A=\dfrac{1+2}{2}-\dfrac{1}{2}=2-\dfrac{1}{2}=\dfrac{3}{2}\)
\(28,\\ \sin^2\alpha=1-\cos^2\alpha=1-\dfrac{1}{2}=\dfrac{1}{2}\\ \Leftrightarrow\sin\alpha=\dfrac{\sqrt{2}}{2}\)