求双曲线X方/9
双曲线x^2/9-y^2/16=1的渐近线是直线y=+'-4x/3，其斜率是tanA=+'-4/3. tan2A=2tanA/[1-(tanA)^2] =2(4/3)/(1-16/9)=-24/7 --->夹角（锐角）为arctan(24/7).