Cho a,b,c khác 0 , a+b+c khác 0 thỏa mãn 1/a + 1/b + 1/c = 1/a+b+c
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15,24 : Hàng đơn vị
50,621 : Hàng chục
12,53 : Hàng phần mười
2,345: Hàng phần nghìn
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\(\frac{2}{\sqrt{3}-1}-\frac{2}{\sqrt{3}+1}\)
\(=\frac{2\left(\sqrt{3}+1\right)}{\left(\sqrt{3}-1\right)\left(\sqrt{3}+1\right)}-\frac{2\left(\sqrt{3}-1\right)}{\left(\sqrt{3}-1\right)\left(\sqrt{3}+1\right)}\)
\(=\frac{2\left(\sqrt{3}+1\right)}{2}-\frac{2\left(\sqrt{3}-1\right)}{2}\)
\(=\sqrt{3}+1-\sqrt{3}+1\)
\(=2\)
\(\frac{2}{\sqrt{3}-1}-\frac{2}{\sqrt{3}+1}.\)
\(=\frac{2\left(\sqrt{3}+1\right)}{\left(\sqrt{3}-1\right)\left(\sqrt{3}+1\right)}-\frac{2\left(\sqrt{3}-1\right)}{\left(\sqrt{3}+1\right)\left(\sqrt{3}-1\right)}.\)
\(=\frac{2\sqrt{3}+2}{\left(\sqrt{3}-1\right)\left(\sqrt{3}+1\right)}-\frac{2\sqrt{3}-2}{\left(\sqrt{3}+1\right)\left(\sqrt{3}-1\right)}.\)
\(=\frac{2\sqrt{3}+2-2\sqrt{3}+2}{\left(\sqrt{3}-1\right)\left(\sqrt{3}+1\right)}\)
\(=\frac{4}{3-1}=\frac{4}{2}=2\)
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Ta có: \(\widehat{A}+\widehat{B}+\widehat{C}=\widehat{C}+10^o+\widehat{C}-10^o+\widehat{C}=3\widehat{C}=180^o\)
\(\Rightarrow\widehat{C}=60^o\)\(\Rightarrow\widehat{A}=70^o\); \(\widehat{B}=50^o\)