If the equation $ax^2 + 2hxy + by^2 + 2gx + 2fy + c = 0$ represents a pair of straight lines,then the square of the distance of their point of intersection from the origin is

What does the cell wall of algae consist of?

Solar radiation emitted by the sun resembles that emitted by a black body at a temperature of $6000\, K$. Maximum intensity is emitted at a wavelength of about $4800\, \mathring{A}$. If the sun was cooled down from $6000\, K$ to $3000\, K$,then the peak intensity would occur at a wavelength of ......... $\mathring{A}$.

If $\alpha = \frac{5}{2! 3} + \frac{5 \cdot 7}{3! 3^2} + \frac{5 \cdot 7 \cdot 9}{4! 3^3} + \ldots$,then $\alpha^2 + 4\alpha$ is equal to

$A$ particle moves along the curve $y=x^2+2x$. The point on the curve such that the $x$ and $y$ coordinates of the particle change at the same rate is

If $y = mx + c$ is a tangent to the ellipse $\frac{x^2}{9} + \frac{y^2}{4} = 1$,then the value of $c$ is