18. tan ( x - pi/4)
This is the graph of the tangent shifted to the right by pi/4 units
The normal tangent graph would have an asymptote at pi/2......so this graph will have an asymptote, for example, at
x = (pi/4 + pi/2) = 3pi/4
See the graph here : https://www.desmos.com/calculator/ufvhykjqvu
19. f(x) = 3cos(2pi *x)
The period, P, can be found as
P(2pi) = 2pi → P = 1 radian
Here's the graph : https://www.desmos.com/calculator/a4od0m3gco