\(\sqrt{\sqrt{5}-\sqrt{3-\sqrt{29-12\sqrt{5}}}}\)

=\(\sqrt{\sqrt{5}-\sqrt{3-\sqrt{3^2-12\sqrt{5}+\left(2\sqrt{5}\right)^2}}}\)

\(=\sqrt{\sqrt{5}-\sqrt{3-\left(3-2\sqrt{5}\right)^2}}\)

\(=\sqrt{\sqrt{5}-\sqrt{6-2\sqrt{5}}}\)

\(=\sqrt{\sqrt{5}-\sqrt{5-2\sqrt{5}+1}}\)

=\(\sqrt{\sqrt{5}-\sqrt{\left(\sqrt{5}-1\right)^2}}\)

\(=\sqrt{\sqrt{5}-\sqrt{5}+1}\)

\(=\sqrt{1}=1\)

\(\sqrt{117,5^2-26,5^2-1440}\)\(=\sqrt{\left(117,5-26.5\right)\left(117.5+26,5\right)-144\cdot10}\)\(=\sqrt{91\cdot144-144\cdot10}\)

\(=\sqrt{144\cdot\left(91-10\right)}\)

\(=\sqrt{144\cdot81}\)

\(=\sqrt{144}\cdot\sqrt{81}\)

\(=12\cdot9=108\)

\(\frac{x}{y+z+t}=\frac{y}{x+z+t}=\frac{z}{x+y+t}=\frac{t}{x+y+z}=\frac{x+y+z+t}{3\left(x+y+z+t\right)}=\frac{1}{3}\)

\(3x=y+z+t\)

\(3y=x+z+t\)

\(3x+3y=x+y+2z+2t\)

\(x+y=z+t\)

Tương tự ta được

\(y+z=x+t\)

P=1+1+1+1=4

\(\sqrt{6+2\sqrt{5}}:\left(1+\sqrt{5}\right)\)

\(=\sqrt{5+2\cdot\sqrt{5}+1}:\left(1+\sqrt{5}\right)\)

\(=\sqrt{\left(\sqrt{5}+1\right)^2}:\left(1+\sqrt{5}\right)\)

= \(\left(\sqrt{5}+1\right):\left(1+\sqrt{5}\right)=1\)

mạch nt hay song song

có sơ đồ ko

vì 2 dây cùng chất liệu nên

\(\rho_1=\rho_2\)

\(\Rightarrow\dfrac{R_1S_1}{l_1}=\dfrac{R_2S_2}{l_2}\)

\(\Rightarrow S_2=\dfrac{R_1S_1l_2}{R_2l_1}=\dfrac{15\cdot0,2\cdot10^{-6}\cdot30}{10\cdot24}\)

\(=0,375\cdot10^{-6}m^2\)

hay 0,375\(mm^2\)

ta có R=\(\rho\dfrac{l}{s}\)

\(\Rightarrow\rho=\dfrac{R\cdot S}{l}=\dfrac{7\cdot0,4\cdot10^{-6}}{100}=2,8\cdot10^{-8}\left(\Omega m\right)\)

quãng đường tàu đi được là S=v.t=30.5=150(km)