Question

3-я задача.
Решение:
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Answer 1

1/R=1/R1+1/R2
1/R1=1/R-1/R2
1/R1=5/9-1/2=10/18-9/18=1/18
R1=18Ом
R=R1+R2
R=1+2=3 Ом