The product of the lengths of the perpendiculars drawn from the foci of the ellipse $\frac{x^2}{9}+\frac{y^2}{25}=1$ to the tangent at any point on the ellipse is

If three points $A, B$ and $C$ have position vectors $(1, x, 3)$,$(3, 4, 7)$ and $(y, -2, -5)$ respectively and if they are collinear,then $(x, y) = $

Assertion: The isothermal curves intersect each other at a certain point.
Reason: The isothermal change takes place slowly,so,the isothermal curves have very little slope.

$A$ wire of length $l$ is bent into a circular coil of one turn of radius $R_1$. Another wire of the same material,same area of cross-section,and same length is bent into a circular coil of two turns of radius $R_2$. When the same current flows through the two coils,the ratio of magnetic induction at the centres of the two coils is

$A$ circle of radius $4$,drawn on a chord of the parabola $y^2 = 8x$ as diameter,touches the axis of the parabola. Then,the slope of the chord is

Which is the most important center for lymph formation?