Respuesta :

evgeniylevi
Try this option:
1. rule: if θ∈(0;90°), then cosθ>0 and sinθ>0;
2. using the rule and sin²θ+cos²θ=1, ⇒ cosθ=√(1-sin²θ)=√15/4.

answer:
[tex] \frac{ \sqrt{15}}{4}.[/tex]