# How do you use transformation to graph the cosine function and determine the amplitude and period of y=-cos(x-pi/4)?

Feb 23, 2018

One of the standard forms of a trig function is y = ACos(Bx + C) + D

#### Explanation:

A is the amplitude (absolute value since it's a distance)

B affects the period via formula Period = $\frac{2 \setminus \pi}{B}$

C is the phase shift

D is the vertical shift

In your case, A = -1, B = 1, C = $- \setminus \frac{\pi}{4}$ D = 0

Period = $\frac{2 \setminus \pi}{B} \to \frac{2 \setminus \pi}{1} \to 2 \setminus \pi$
Phase shift = $\setminus \frac{\pi}{4}$ to the RIGHT (not the left as you might think)