6.
\(=>I2=\dfrac{U2}{R2}=>0,75=\dfrac{30}{2R1}=>R1=20\left(om\right)\)
\(=>R2=2R1=40\left(om\right)\)
\(=>U1=I1.R1=20.0,5=10V\)
7. R1 nt R2 nt R3
a,\(=>Im=\dfrac{Uab}{Rtd}=\dfrac{36}{R1+R2+R3}=\dfrac{36}{3+8+7}=2A\)
b,\(=>Im'=\dfrac{1}{2}Im=\dfrac{1}{2}.2=1A\)
\(1=\dfrac{Uab}{R1+R2+R'}=>1=\dfrac{36}{11+R'}=>R'=25\left(om\right)\)
8 R1 nt R2
\(U2=3U1=>I2.R2=3I1.R1=>R2=3R1\)
\(=>Rtd=R1+R2=4R1=\dfrac{U}{I}=\dfrac{60}{4}=>R1=3,75\left(om\right)\)
\(=>R2=3R1=11,25\left(om\right)\)
\(=>U1=IR1=3,75.4=15V=>U2=IR2=45V\)
9. không thấy hình