mechanics is going really tough for me. i can't solve innovative problems even after clearing the concepts. what should i do?

Two lines are inclined at angle 'a' each parallel to each other. A ball is projected from the midpoint of both lines at an angle 'b' with the direction of the lines. The ball just touches one line and hits the other line perpendicularly. Prove that tan b = (√2 - 1) tan a

Is 75pecent criteria required overall 

If a person don't have 75 in pcm aggregate and individually too in pcm

But have pcmEngPhyed /500 aggregate overall to be 75 

Will he be eligible for iits nits?

For the gas phase reaction SO3(g) SO2 (g) + ½ O2 (g) if the gaseous mixture in a closed container is allowed to come at equilibrium and the degree of dissociation (α) at equilibrium is found to be 2/3 at 400 K and 1 atm pressure then calculate the vapour density of the equilibrium mixture.

For the gas phase reaction SO3(g) SO2 (g) + ½ O2 (g) if the gaseous mixture in a closed container is allowed to come at equilibrium and the degree of dissociation (α) at equilibrium is found to be 2/3 at 400 K and 1 atm pressure then calculate the vapour density of the equilibrium mixture.40013060

Let S={x:x belongs to R(√3+√2)^(x^2-4) - (√3-√2)^(x^2-4)=10}. Then n(S) is equal to-