If f(θ)=sinâ¡Î¸(sinâ¡Î¸+sinâ¡3θ), then f(θ)
â¥0 only when θâ¥0
â¤0 for all real θ
â¥0 for all real θ
â¤0 when only θ â¤0
f(θ)=sinâ¡Î¸sinâ¡Î¸+3sinâ¡Î¸â4sin3â¡Î¸=4sin2â¡Î¸1âsin2â¡Î¸=sin2â¡2θâ¥0 for all real θ.