解:支反力R4 M() n RA-RB=m// ro(r) R 1/21/2RBO=R MERx= x(0<x≤l/2) Q 12 mM(c) 717 O=R M n M=Rx-m m/2 R o() (-1) (l/2≤x<l) g=m/I, M=m/2 max解：支反力 R R m l A = − B = , lm Q = R A = x lm M R x = A = ( 0 ＜ x ＜ l 2 ) lm Q = R A = M = RA x − m = ( − 1 ) lx m ( l 2 ＜ x ＜ l ) Q m l M m 2 − m 2 , 2 max max Q = m l M = m l 2 l 2 m RA R B Q (x )M(x ) x n RA Q (x ) m M(x ) l 2x RA n