在直角坐标系xoy中，点P到两点(-
（1）写出C的方程； （2）求证：-1＜
|
（1）由题意可得，点P是以P(-
，0)，(3
，0)为焦点的椭圆，且2a=43
∴a=2，c=
，b2=a2-c2=13
曲线C的方程为
+y2=1x2 4
（2）联立方程
可得（1+4k2）x2+16kx+12=0y=kx+2
+y2=1x2 4
由△=4k2-3＞0可得k2＞3 4
设A（x1，y1）B（x2，y2） x1+x2=-
x1x2=16k 1+4k2 12 1+4k2
∵
•OA
=x1x2+y1y2=（1+k2）x1x2+2k（x1+x2）+4OB
=(1+k2)•
+2k•12 1+4k2
+4=-16k 1+4k2 16-4k2 1+4k2
令y=
则可得k2=16-4k2 1+4k2
＞16-y 4(y+1) 3 4
∴-1＜y＜
即-1＜13 4
•OA
＜OB 13 4
| A federal judge on Monday certified a $200 billion class action lawsuit against the tobacco industry for its marketing of light cigarettes. Eastern District of New York Judge Jack B. Weinstein’s 540-page opinion in Schwab v. Philip Morris USA, Inc., 04-CIV-1945—which included an additional 965 pages of appendices for a total of 1,505 pages—gave tens of millions of smokers an avenue to recover damages from the nation’s largest tobacco companies, including Philip Morris USA Inc., R.J. Reynolds Tobacco Co., Lorillard Tobacco Co., and Liggett Group, Inc. The class will include anyone who purchased light cigarettes from the time tobacco companies began selling them in the 1970s. The judge said he even would consider broadening the class, to encompass smokers of all "low tar" brands, not just light cigarettes. The judge suggested that an expansion of the class could assist the parties in negotiating a global settlement. He set a trial date for January 22, 2007. The plaintiffs intend to seek treble damages. einstein has expressed skepticism about the plaintiffs’ theory of damages, which alleges that light smokers were defrauded of billions because they believed they were buying a product of greater value because of its health advantages. The judge also questioned the size of the class, as well as the claim that as many as 90 percent of light cigarette smokers chose the cigarettes because they were less harmful. In his ruling Monday, the judge stressed that while the suit was far from perfect, the evidence was sufficient. He said the jury system—which he described as the "ultimate focus group of the law"—was well equipped to sort out the particulars in accordance with Amendment Ⅶ of the U.S. Constitution. Weinstein declined to grant an interlocutory appeal to the 2nd U.S. Circuit Court of Appeals. Theodore M. Grossman of Jones Day in Cleveland, which represents R.J. Reynolds, said the defendants would seek a stay and appeal the class certification under Rule 23(f)of the Federal Rules of Civil Procedure. |
The phrase "product of greater value" underlined in Paragraph 4 refers to ______ .
A．lawsuit plaintiffs
B．theoretical damages
C．light cigarettes
D．health advantages