## Functions of the form \(y = \cos \theta\) for \(\text{0}\text{°} \leq \theta \leq \text{360}\text{°}\)

The period is \(\text{360}\text{°}\) and the amplitude is \(\text{1}\).

Domain: \([\text{0}\text{°};\text{360}\text{°}]\)

For \(y = \cos \theta\), the domain is \(\{ \theta: \theta \in \mathbb{R} \}\), however in this case, the domain has been restricted to the interval \(\text{0}\text{°} \leq \theta \leq \text{360}\text{°}\).

Range: \([-1;1]\)

\(x\)-intercepts: \((\text{90}\text{°};0)\), \((\text{270}\text{°};0)\)

\(y\)-intercept: \((\text{0}\text{°};1)\)

Maximum turning points: \((\text{0}\text{°};1)\), \((\text{360}\text{°};1)\)

Minimum turning point: \((\text{180}\text{°};-1)\)

## Functions of the form \(y = a \cos \theta + q\)

Cosine functions of the general form \(y = a \cos \theta + q\), where \(a\) and \(q\) are constants.

**The effects of \(a\) and \(q\) on \(f(\theta) = a \cos \theta + q\):**

**The effect of \(q\) on vertical shift**For \(q>0\), \(f(\theta)\) is shifted vertically upwards by \(q\) units.

For \(q<0\), \(f(\theta)\) is shifted vertically downwards by \(q\) units.

**The effect of \(a\) on shape**For \(a>1\), the amplitude of \(f(\theta)\) increases.

For \(0<a<1\), the amplitude of \(f(\theta)\) decreases.

For \(a<0\), there is a reflection about the \(x\)-axis.

For \(-1 < a < 0\), there is a reflection about the \(x\)-axis and the amplitude decreases.

For \(a < -1\), there is a reflection about the \(x\)-axis and the amplitude increases.