A vertical translation means that we move a base function (a function with no numbers) up or down on the y-axis. In other words, we change the starting and ending points for the y. The amplitude, period, and degrees on the x-axis stay the same - only the y-axis changes.
We see a vertical translation whenever there is a number added or subtracted at the end of the function. For example: y = sinx + 2 means that we would take the basic graph of y = sinx and move the whole function up 2 units on the y-axis. Instead of starting at (0, 0), we would start at (0, 2).
For cosine, it's a bit trickier because the graph of cosine begins at (0,1) instead of (0,0). Therefore, for the graph of y = cosx + 2, we would start at positive 3 instead of positive 2 because cosine already starts at 1, so we have to move the graph up two units from where it already starts.
IMPORTANT NOTE: just because we have a vertical translation, does not mean the amplitude of the function changes. Unless we see a number in front of the function, the amplitude would still be 1. However, if we do see a number in front of the function, such as y = 2sinx + 2, then we would have a vertical translation as well as a change in amplitude (because there is a number in front of the trig function).
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