Prévia do material em texto
185
𝑸𝒖𝒆𝒔𝒕ã𝒐 𝟏.
𝑎) 𝑆𝑒𝑗𝑎 𝑓: [0,2018] → ℝ 𝑐𝑜𝑛𝑡í𝑛𝑢𝑎 𝑒𝑚 [0,2018] 𝑒 𝑑𝑒𝑟𝑖𝑣á𝑣𝑒𝑙 𝑒𝑚 (0,2018) 𝑠𝑎𝑡𝑖𝑠𝑓𝑎𝑧𝑒𝑛𝑑𝑜
𝑓 ′(𝑥)𝑓 ′(2018 − 𝑥) ≤ 0 ∀𝑥 ∈ (0,2018).𝑆𝑎𝑏𝑒𝑛𝑑𝑜 𝑞𝑢𝑒 𝑒𝑥𝑖𝑠𝑡𝑒 𝑛𝑜 𝑚á𝑥𝑖𝑚𝑜 𝑢𝑚 𝑐 𝑡𝑎𝑙 𝑞𝑢𝑒
𝑓 ′(𝑐) = 0 𝑒 𝑞𝑢𝑒 𝑓 ′′(𝑐) > 0, 𝑠𝑒 𝑓 ′(𝑐) = 0 𝑒𝑛𝑐𝑜𝑛𝑡𝑟𝑒 𝑜𝑠 𝑖𝑛𝑡𝑒𝑟𝑣𝑎𝑙𝑜𝑠 𝑜𝑛𝑑𝑒 𝑓 é 𝑐𝑟𝑒𝑠𝑐𝑒𝑛𝑡𝑒
𝑒 𝑑𝑒𝑐𝑟𝑒𝑠𝑐𝑒𝑛𝑡𝑒.
𝑆𝑒 𝑓 ′(𝑐) = 0, 𝑒𝑛𝑡ã𝑜 𝑐 é 𝑢𝑚 𝑛ú𝑚𝑒𝑟𝑜 𝑐𝑟í𝑡𝑖𝑐𝑜 𝑑𝑒 𝑓 𝑒𝑚 (0,2018) 𝑒 𝑐𝑜𝑚𝑜 𝑓′′(𝑐) > 0,
𝑝𝑒𝑙𝑜 𝑇𝑒𝑠𝑡𝑒 𝑑𝑎 𝑆𝑒𝑔𝑢𝑛𝑑𝑎 𝐷𝑒𝑟𝑖𝑣𝑎𝑑𝑎 (𝑐,𝑓(𝑐)) é 𝑢𝑚 𝑝𝑜𝑛𝑡𝑜 𝑑𝑒 𝑚í𝑛𝑖𝑚𝑜 𝑙𝑜𝑐𝑎𝑙 𝑒, 𝑐𝑜𝑚
𝑖𝑠𝑠𝑜, 𝑝𝑎𝑟𝑎 𝑥 ∈ (0,𝑐) 𝑡𝑒𝑚𝑜𝑠 𝑓 ′(𝑥) 0.
𝐶𝑜𝑛𝑡𝑢𝑑𝑜, 𝑎 𝑒𝑥𝑝𝑟𝑒𝑠𝑠ã𝑜 𝑓′(𝑥)𝑓 ′(2018− 𝑥) ≤ 0 𝑛𝑜𝑠 𝑓𝑜𝑟𝑛𝑒𝑐𝑒 𝑝𝑎𝑟𝑎 𝑜 𝑣𝑎𝑙𝑜𝑟 𝑚é𝑑𝑖𝑜
𝑑𝑜 𝑖𝑛𝑡𝑒𝑟𝑣𝑎𝑙𝑜,𝑥 = 1009, 𝑎 𝑠𝑒𝑔𝑢𝑖𝑛𝑡𝑒 𝑖𝑛𝑒𝑞𝑢𝑎çã𝑜:
𝑓 ′(1009).𝑓 ′(2018− 1009) ≤ 0
[𝑓 ′(1009)]2 ≤ 0
∴ 𝑓 ′(1009) = 0 ⟹ 𝑐 = 1009.
𝐿𝑜𝑔𝑜, 𝑓 é 𝑐𝑟𝑒𝑠𝑐𝑒𝑛𝑡𝑒 𝑒𝑚 (1009,2018) 𝑒 𝑑𝑒𝑐𝑟𝑒𝑠𝑐𝑒𝑛𝑡𝑒 𝑒𝑚 (0,1009).
𝑏) 𝑆𝑒𝑗𝑎 𝑓(𝑥) = ln(1 − ln 𝑥) . 𝐷𝑒𝑡𝑒𝑟𝑚𝑖𝑛𝑒 𝑜 𝑑𝑜𝑚í𝑛𝑖𝑜, 𝑜𝑠 𝑖𝑛𝑡𝑒𝑟𝑣𝑎𝑙𝑜𝑠 𝑑𝑒 𝑐𝑟𝑒𝑠𝑐𝑖𝑚𝑒𝑛𝑡𝑜 𝑒
𝑑𝑒𝑐𝑟𝑒𝑠𝑐𝑖𝑚𝑒𝑛𝑡𝑜 , 𝑎 𝑐𝑜𝑛𝑐𝑎𝑣𝑖𝑑𝑎𝑑𝑒 𝑒 𝑜𝑠 𝑝𝑜𝑛𝑡𝑜𝑠 𝑑𝑒 𝑖𝑛𝑓𝑙𝑒𝑥ã𝑜 𝑑𝑒 𝑓.
𝐷𝑜𝑚í𝑛𝑖𝑜 𝑑𝑒 𝑓: 𝐷(𝑓) = {𝑥 ∈ ℝ |0 0 𝑒,
𝑓 é 𝑑𝑒𝑐𝑟𝑒𝑠𝑐𝑒𝑛𝑡𝑒 𝑜𝑛𝑑𝑒 𝑓 ′ 0 𝑒 𝑐𝑜𝑛𝑐𝑎𝑣𝑖𝑑𝑎𝑑𝑒 𝑣𝑜𝑙𝑡𝑎𝑑𝑎
𝑝𝑎𝑟𝑎 𝑏𝑎𝑖𝑥𝑜 𝑜𝑛𝑑𝑒 𝑓 ′′