A graph represents a function of the form $\displaystyle{y}={a}{\sin{{b}}}{x}\usepackage{cmbright}\Huge\$ or $\displaystyle{y}={a}{\cos{{b}}}{x}\usepackage{cmbright}\Huge\$ , where a and b are nonzero constants. The graph has a hill on the interval $\displaystyle{\left[-\pi,{0}\right]}\usepackage{cmbright}\Huge\$ . Which statement is true?