设0
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设0设0设01/cost+a/(1-cost)=16,1-cost+acost=16cost-16cos²t,16cos²t+(a-17)cost+1=0,Δ=(a-17)
设0
设0
设0
1/cost + a/(1-cos t)=16,1-cos t+acost=16cost-16cos²t,16cos²t+(a-17)cost+1=0,
Δ=(a-17)²-64≥0,a≥25或a≤9,∵0
("1"的代换)“cost+1-cost=1"
f(t)=(1/cos t + a/(1-cos t))(cost+1-cost)
接下去用不等式