Cho dãy số (un)({u_n})(un) với un=(1−122).(1−132)...(1−1n2){u_n} = \left( {1 - \dfrac{1}{{{2^2}}}} \right).\left( {1 - \dfrac{1}{{{3^2}}}} \right)...\left( {1 - \dfrac{1}{{{n^2}}}} \right)un=(1−221).(1−321)...(1−n21). Khi đó limun\lim {u_n}limunbằng?
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