(2) When the slider moves to the midpoint, U/(R 1+20+0.5R)=0.45? ———②

(3) When the slider moves to the A end,? u/(r 1+20)= 9/r 1————③

By who? ① and ③, can you find them? R=2R 1+40？ . Replace this value with? ①、②? Re-simplification of the equation after the merger of the two expressions;

r 1^2+ 10r 1-200=0？ . Can become. (R 1+5)^2=225？ . Solve? r 1 = 10ω？ And r 1 =-20ω=-20ω (give up! )。

Second, R=2R 1+40=60? (Ω)。

Three. u = 9(r 1+20)/r 1 = 9( 10+20)/ 10 = 27(v)。

Hope to adopt! thank you