# Graph question

• Jan 24th 2009, 07:00 AM
ally79
Graph question
Sketch the graph of y=cos x in the range -pi < or equal to x < or equal to pi
Hence sketch the graph of y=|cos X| in the same range.

From my knowledge of sine and cosine waves i know what the graph will look like, and what the modulus graph will look like, what i dont know is how to prove it. i substituted pi and -pi into cosx and got -1 for both points on the graph, nbut i cant remember how t prove where the turning point is, i know its at (0,1) but i cant prove that without using prior knowledge,

• Jan 24th 2009, 07:03 AM
Mush
Quote:

Originally Posted by ally79
Sketch the graph of y=cos x in the range -pi < or equal to x < or equal to pi
Hence sketch the graph of y=|cos X| in the same range.

From my knowledge of sine and cosine waves i know what the graph will look like, and what the modulus graph will look like, what i dont know is how to prove it. i substituted pi and -pi into cosx and got -1 for both points on the graph, nbut i cant remember how t prove where the turning point is, i know its at (0,1) but i cant prove that without using prior knowledge,