2023年高考数学天津12 |
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2023-07-08 14:19:41 |
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(5分)过原点的一条直线与圆$C:(x+2)^{2}+y^{2}=3$相切,交曲线$y^{2}=2px(p > 0)$于点$P$,若$\vert OP\vert =8$,则$p$的值为 ____. 答案:6. 分析:不妨设直线方程为$y=kx(k > 0)$,由直线与圆相切求解$k$值,可得直线方程,联立直线与抛物线方程,求得$P$点坐标,再由$\vert OP\vert =8$列式求解$p$的值. 解:如图,
由题意,不妨设直线方程为$y=kx(k > 0)$,即$kx-y=0$, 由圆$C:(x+2)^{2}+y^{2}=3$的圆心$C(-2,0)$到$kx-y=0$的距离为$\sqrt{3}$, 得$\dfrac{\vert -2k\vert }{\sqrt{{k}^{2}+1}}=\sqrt{3}$,解得$k=\sqrt{3}(k > 0)$, 则直线方程为$y=\sqrt{3}x$, 联立$\left\{\begin{array}{l}{y=\sqrt{3}x}\\ {{y}^{2}=2px}\end{array}\right.$,得$\left\{\begin{array}{l}{x=0}\\ {y=0}\end{array}\right.$或$\left\{\begin{array}{l}{x=\dfrac{2p}{3}}\\ {y=\dfrac{2\sqrt{3}p}{3}}\end{array}\right.$,即$P(\dfrac{2p}{3},\dfrac{2\sqrt{3}p}{3})$. 可得$\vert OP\vert =\sqrt{(\dfrac{2p}{3})^{2}+(\dfrac{2\sqrt{3}p}{3})^{2}}=8$,解得$p=6$. 故答案为:6. 点评:本题考查直线与圆、直线与抛物线位置关系的应用,考查运算求解能力,是中档题.
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