Question

如图，求极限

Answer 1

（x→∞）lim [cos²3x/cos²x]
= （x→∞）lim [(4cos³x-3cosx)²/cos²x]
= （x→∞）lim [(4cos²x-3)²]
= （x→∞）lim [(4cos²x-2-1)²]
= （x→∞）lim [(2cos2x-1)²]

= （x→∞）lim [4cos²2x-4cos2x+1]
震荡不存在。