1、当P从O运动到A
S=1/2*OP*CO=1/2*4*t=2t (0
S=S梯形DBAO - S△OPA-S△DPB
=1/2*(3+6)*4-1/2*6*t-1/2*3*(4-t)
=12-3t/2 (6
S=1/2*BD*CO=1/2*4*(3-t)
=6-2t (10≤t<13)