若a=1/log519+2/log319+3/log219,求证:1﹤a﹤2.
证明a=1/log519+2/log319+3/log219 =log195+2log193+3log192 =log195×9×8=log19360 因为19﹤360﹤361=192, 所以log1919﹤log19360﹤log19361, 所以1﹤a﹤2.
若a=1/log519+2/log319+3/log219,求证:1﹤a﹤2.
证明a=1/log519+2/log319+3/log219 =log195+2log193+3log192 =log195×9×8=log19360 因为19﹤360﹤361=192, 所以log1919﹤log19360﹤log19361, 所以1﹤a﹤2.