follows from the fact that the cosine function is
-periodic, which means
. Roughly speaking, this is the same as saying that a point on a circle is the same as the point you get by completing a full revolution around the circle (i.e. add
to the original point's angle with respect to the horizontal axis).
If you make another complete revolution (so we're effectively adding
) we get the same result:
. This is true for any number of complete revolutions, so that this pattern holds for any even multiple of
added to the argument. Therefore
for any integer
.
Next, because
, it follows that
is also true for any integer
. So we have
The rest follows from considering either case and solving for
.
First answer should be correct ..
The answers would be pyramid and triangular prism.
7.5 i think not 100% sure tho