如圖,設(shè)P是圓x
2+y
2=12上的動(dòng)點(diǎn),點(diǎn)D是點(diǎn)P在x軸上的射影,點(diǎn)M在DP的延長(zhǎng)線上,且
.
(1)當(dāng)點(diǎn)P在圓上運(yùn)動(dòng)時(shí),求動(dòng)點(diǎn)M的軌跡方程;
(2)記動(dòng)點(diǎn)M的軌跡為曲線C,過(guò)點(diǎn)P(3,2)作兩條相異直線分別與曲線C相交于A,B兩點(diǎn),若直線PA,PB的斜率分別為k
1,k
2,且k
1+k
2=0,試判斷直線AB的斜率是否為定值?并說(shuō)明理由.