Properties of Real Sine Function

From ProofWiki
Jump to: navigation, search

Theorem

Let $x \in \R$ be a real number.

Let $\sin x$ be the sine of $x$.


Then:

Real Sine Function is Continuous

$\sin x$ is continuous on $\R$.


Sine Function is Absolutely Convergent

$\sin x$ is absolutely convergent for all $x \in \R$.


Sine of Zero is Zero

$\sin 0 = 0$


Sine Function is Odd

$\map \sin {-z} = -\sin z$

That is, the sine function is odd.


Sine of Multiple of Pi

$\forall n \in \Z: \sin n \pi = 0$


Sine of Half-Integer Multiple of Pi

$\forall n \in \Z: \map \sin {n + \dfrac 1 2} \pi = \paren {-1}^n$


Shape of Sine Function

The sine function is:

$(1): \quad$ strictly increasing on the interval $\closedint {-\dfrac \pi 2} {\dfrac \pi 2}$
$(2): \quad$ strictly decreasing on the interval $\closedint {\dfrac \pi 2} {\dfrac {3 \pi} 2}$
$(3): \quad$ concave on the interval $\closedint 0 \pi$
$(4): \quad$ convex on the interval $\closedint \pi {2 \pi}$


Also see