Given f(x) = 6x tan x and the interval −π/2 < x < π/2, we know that tan x has asymptotes in both extremes of the interval. To find the vertical asymptotes we evaluate the limit in the x-values we think asymptote can appear, in this case for x = −π/2 and x = π/2.
Then, x = −π/2 and x = π/2 are vertical asymptotes.