Thread: Help with Cosine Function

What function is y = cos(x + π) equal to

can you also explain the answer

thanks

Use the angle-sum identity for cosine:



You may also think of the unit circle. Pick an arbitrary point on the circle. The counter-clockwise angle to the radius at this point as measured from the positive x-axis is the angle . The x-coordinate of this point is . To add radians to this angle, go to the point on the opposite side of the circle, on the other end of the diameter. Can you see what relation the new x-coordinate will always have with the original?

Whenever you add to the input you shift it to the left by Pi/2, so when you add Pi, you do that twice, so you effectively move from cos to -cos. So