pi >= 2 cos(𝑥)−1=−∫𝑥0sin(𝑡)𝑑𝑡 ⟹2=∫𝜋0sin(𝑡)𝑑𝑡≤∫𝜋0𝑡𝑑𝑡=𝑡22|𝜋0=𝜋22 ⟹4≤𝜋2⟹2≤𝜋 □ pi >= 2 sqrt(2) There is a simple way to do it with graph So clearly, 2𝜋≥4√2⟹𝜋≥2√2
