- Home
- Standard 11
- Mathematics
ધારોકે $C: x^2+y^2=4$ અને $C^{\prime}: x^2+y^2-4 \lambda x+9=0$ એ બે વર્તુળો છે. જો વર્તુળો $C^{\prime \prime}$ અને $C^{\prime}$ બે ભિન્ન બિંદુઓમાં છેદે તેવી $\lambda$ ની તમામ કિંમતોનો ગણ ${R}-[a, b]$ હોય, તો બિંદુ $(8 a+12,16 b-20)$ એ_____________ વક્ર પર આવેલું છે.
$x^2+2 y^2-5 x+6 y=3$
$5 x^2-y=-11$
$x^2-4 y^2=7$
$6 x^2+y^2=42$
Solution
$x^2+y^2=4$
$C(0,0) \quad \quad r_1=2$
$C^{\prime}(2 \lambda, 0) \quad r_2=\sqrt{4 \lambda^2-9}$
$\left|\mathrm{r}_1-\mathrm{r}_2\right|<\mathrm{CC} \mathrm{C}^{\prime}<\left|\mathrm{r}_1+\mathrm{r}_2\right|$
$\left|2-\sqrt{4 \lambda^2-9}\right|<|2 \lambda|<2+\sqrt{4 \lambda^2-9}$
$4+4 \lambda^2-9-4 \sqrt{4 \lambda^2-9}<4 \lambda^2$
True$\lambda \in$ R…. $(1)$
$4 \lambda^2<4+4 \lambda^2-9+4 \sqrt{4 \lambda^2-9}$
$5<4 \sqrt{4 \lambda^2-9} \text { and } \quad \lambda^2 \geq \frac{9}{4}$
$\frac{25}{16}<4 \lambda^2-9 \quad \lambda \in\left(-\infty,-\frac{3}{2}\right] \cup\left[\frac{3}{2}, \infty\right)$
$\frac{169}{64}<\lambda^2$
$\lambda \in\left(-\infty,-\frac{13}{8}\right) \cup\left(\frac{13}{8}, \infty\right)$ $…(2)$
from $(1) $and $(2)$$\lambda \in$
$\lambda \in\left(-\infty,-\frac{13}{8}\right) \cup\left(\frac{13}{8}, \infty\right) \Rightarrow R-\left[-\frac{13}{8}, \frac{13}{8}\right]$
as per question $a=-\frac{13}{8}$ and $b=\frac{13}{8}$
$\therefore \quad$ required point is $(-1,6)$ with satisfies option $(4)$