tanA + tanB = p …(1)

tanA tanB = q

1 – tanA tanB = 1 – q …(2)

eq(1) ፥ eq(2)

use formula tan(A+B) :

tan(A + B) = [ tanA + tanB]/[1 – tanA tanB]

⇒ tan(A + B) = [p]/[1 – q]

Now convert this tan(A + B) into sin(A + B)

⇒ sin^{2}(A + B) = [p]/[p^{2} + (1- q)^{2}]

## Arpita

When n=1 then only 1s2 possible so no of electron = 2

When n=2 then 2s2, 2p6 possible so no of electron = 8

When n=3 then 3s2, 3p6, 3d10 possible so no of electron = 18

n = 4 and above not possible so no of total no of electron = 28

total electron = total element = 28