Question

一道数学动点问题，好难啊，帮我做一下谢谢

只需2，3问，谢谢

Answer 1

（2）若P 在AB上且Q在CB上， S=(8-t)(6-2t)/2=t²-11t+24 (t＜3)
若P 在CB上且Q在AB上， S=(t-8)(2t-6)/2=t²-11t+24 (3＜t＜7)
∴S=t²-11t+24 t∈(3,7)
(3)AP=QB t=2t-6
∴t=6

Answer 2

点P从A到D用22s,点Q从C到D用10s,
(2)0<=t<=3时P在AB,Q在CD,
PB=8-t,QB=6-2t,
S=（1/2）（8-t)(6-2t)=(8-t)(3-t)=24-11t+t^2.
3<t<=7时P,Q都在AB,S=0.
7<t<=8时P在AB,Q在AD,BP=8-t,AQ=2(t-7),
S=(8-t)(t-7)=-t^2+15t-56.
8<t<=14时P在BC,Q在AD,BP=t-8,
S=(1/2)BP*AB=4(t-8).
14<t<=22时P在CD,Q与D重合，S=0.
综上，S={(8-t)(3-t),0<=t<=3;
{0,3<t<=7,或14<t<=22;
{(8-t)(t-7),7<t<=8;
{4(t-8),8<t<=14.
(3)t=2.