X varies directly as a product of u and v and inversely s thoer sum . If x=3 when u=3andv=1 find (a) the relationship connecting x,u,v (b). What is the value of x if u=3andv=3?

Answer 1

x = k u v/(u+v)

3 = k 3*1 /(4)
so
k = 4
so
x = 4 u v / (u+v)
so put in 3 for u and 3 for v
4*9/6

Answer 2

The answer is 21