Vout= Vin* [98+((2/k)*Vin)]

I think im right so far in thinking il end up with;

Vin*98 + Vin*(2/k) + Vin*Vin

Now if thats right, then for the 3rd part of the equation were

Vin= 0.01 sin(2pi800)

i get an equation of the type

(sinx)*(siny)= cos(x-y) - cos(x+y)

How do i apply this to 0.001 sin (2pi800) ? i.e what do i do with the two 0.001's etc?

Please help im very lost