题目

Lions are opportunists. They prefer to eat without having to do too much work. When resting in the shade, they are also watching the sky to see what is flying by, and even in the heat of the day they will suddenly start up and run a mile across the plains to find out what is going on. If another animal has made a kill, they will drive it off and take the dill for themselves. A grown lion can easily eat 60 pounds of meat at a single feeding. Often they eat until it seems painful for them to lie down. The lionesses (母狮) , being thinner and faster, are better hunters (猎手) than the m已知向量=（k，12），=（4，5），=（10，k）．（1）若A，B，C三点共线，求实数k的值；（2）若A，B，C构成直角三角形，求实数k的值．