Let (x + 10)⁵⁰ + (x $$-$$ 10)⁵⁰ = a₀ + a₁x + a₂x² + . . . . + a₅₀x⁵⁰, for all x $$ \in $$ R; then $${{{a_2}} \over {{a_0}}}$$ is equal to

The sum of the real values of x for which the middle term in the binomial expansion of $${\left( {{{{x^3}} \over 3} + {3 \over x}} \right)^8}$$ equals 5670 is :

The value of r for which ²⁰C_r ²⁰C₀ + ²⁰C_r$$-$$1 ²⁰C₁ + ²⁰C_r$$-$$2 ²⁰C₂ + . . . . .+ ²⁰C₀ ²⁰C_r  is maximum, is

The positive value of $$\lambda $$ for which the co-efficient of x² in the expression x² $${\left( {\sqrt x + {\lambda \over {{x^2}}}} \right)^{10}}$$ is 720, is -