If e₁ and e₂ are the eccentricities of the ellipse, $${{{x^2}} \over {18}} + {{{y^2}} \over 4} = 1$$ and the hyperbola, $${{{x^2}} \over 9} - {{{y^2}} \over 4} = 1$$ respectively and (e₁, e₂) is a point on the ellipse, 15x² + 3y² = k, then k is equal to :

Let ƒ be any function continuous on [a, b] and twice differentiable on (a, b). If for all x $$ \in $$ (a, b), ƒ'(x) > 0 and ƒ''(x) < 0, then for any c $$ \in $$ (a, b), $${{f(c) - f(a)} \over {f(b) - f(c)}}$$ is greater than :

The value of
$${\cos ^3}\left( {{\pi \over 8}} \right)$$$${\cos}\left( {{3\pi \over 8}} \right)$$+$${\sin ^3}\left( {{\pi \over 8}} \right)$$$${\sin}\left( {{3\pi \over 8}} \right)$$
is :

Let the observations x_i (1 $$ \le $$ i $$ \le $$ 10) satisfy the
equations, $$\sum\limits_{i = 1}^{10} {\left( {{x_1} - 5} \right)} $$ = 10 and $$\sum\limits_{i = 1}^{10} {{{\left( {{x_1} - 5} \right)}^2}} $$ = 40.
If $$\mu $$ and $$\lambda $$ are the mean and the variance of the
observations, x₁ – 3, x₂ – 3, ...., x₁₀ – 3, then
the ordered pair ($$\mu $$, $$\lambda $$) is equal to :