[tex]\qquad\qquad\huge\underline{{\sf Answer}}♨[/tex]
The required equation is :
[tex]\qquad \rm \dashrightarrow \:y =a \cos(bx) + k[/tex]
Now, let's find the required values :
period (p) = 6
[distance between any successive Crest or trough]
a = - 4 (flipped)
b = 2π/p = 2π/6 = π/3
k = -2
Distance of starting position from origin = k
Now, plug in the values ~
[tex]\qquad \rm \dashrightarrow \: - 4 \cos( \frac{\pi}{3} x) - 2[/tex]
