1.【阅读思考】
根据绝对值的运算性质可知,一个正数的绝对值是其本身,一个负数的绝对值是其相反数,0的绝对值是0,由此可知,求一个算式整体的绝对值,可先判断整体的正负性,再求它的绝对值,最后化简。
例如:$|7 + 8| = 7 + 8$,$|5 - 7| = -(5 - 7) = 7 - 5$,$|7 - 4| = 7 - 4$。
【牛刀小试】(1)根据上述材料,把下列各式去掉绝对值符号,不要算出最后结果:
$|3 - 10| = $
【拓展延伸】(2)$|\frac{1}{101} - \frac{1}{100}| + |\frac{1}{102} - \frac{1}{101}| + |\frac{1}{103} - \frac{1}{102}| + … + |\frac{1}{1000} - \frac{1}{999}|$。
解:|$\frac{1}{101}$−$\frac{1}{100}$|+|$\frac{1}{102}$−$\frac{1}{101}$|+|$\frac{1}{103}$−$\frac{1}{102}$|+…+|$\frac{1}{1000}$−$\frac{1}{999}$|
=−($\frac{1}{101}$−$\frac{1}{100}$)−($\frac{1}{102}$−$\frac{1}{101}$)−($\frac{1}{103}$−$\frac{1}{102}$)−…−($\frac{1}{1000}$−$\frac{1}{999}$)
=$\frac{1}{100}$−$\frac{1}{101}$+$\frac{1}{101}$−$\frac{1}{102}$+$\frac{1}{102}$−$\frac{1}{103}$+…+$\frac{1}{999}$−$\frac{1}{1000}$
=$\frac{1}{100}$−$\frac{1}{1000}$
=$\frac{9}{1000}$.
根据绝对值的运算性质可知,一个正数的绝对值是其本身,一个负数的绝对值是其相反数,0的绝对值是0,由此可知,求一个算式整体的绝对值,可先判断整体的正负性,再求它的绝对值,最后化简。
例如:$|7 + 8| = 7 + 8$,$|5 - 7| = -(5 - 7) = 7 - 5$,$|7 - 4| = 7 - 4$。
【牛刀小试】(1)根据上述材料,把下列各式去掉绝对值符号,不要算出最后结果:
$|3 - 10| = $
10−3
,$|\frac{3}{14} - \frac{3}{17}| = $$\frac{3}{14}$−$\frac{3}{17}$
;【拓展延伸】(2)$|\frac{1}{101} - \frac{1}{100}| + |\frac{1}{102} - \frac{1}{101}| + |\frac{1}{103} - \frac{1}{102}| + … + |\frac{1}{1000} - \frac{1}{999}|$。
解:|$\frac{1}{101}$−$\frac{1}{100}$|+|$\frac{1}{102}$−$\frac{1}{101}$|+|$\frac{1}{103}$−$\frac{1}{102}$|+…+|$\frac{1}{1000}$−$\frac{1}{999}$|
=−($\frac{1}{101}$−$\frac{1}{100}$)−($\frac{1}{102}$−$\frac{1}{101}$)−($\frac{1}{103}$−$\frac{1}{102}$)−…−($\frac{1}{1000}$−$\frac{1}{999}$)
=$\frac{1}{100}$−$\frac{1}{101}$+$\frac{1}{101}$−$\frac{1}{102}$+$\frac{1}{102}$−$\frac{1}{103}$+…+$\frac{1}{999}$−$\frac{1}{1000}$
=$\frac{1}{100}$−$\frac{1}{1000}$
=$\frac{9}{1000}$.
答案:1.(1)10−3 $\frac{3}{14}$−$\frac{3}{17}$
(2)解:|$\frac{1}{101}$−$\frac{1}{100}$|+|$\frac{1}{102}$−$\frac{1}{101}$|+|$\frac{1}{103}$−$\frac{1}{102}$|+…+|$\frac{1}{1000}$−$\frac{1}{999}$|
=−($\frac{1}{101}$−$\frac{1}{100}$)−($\frac{1}{102}$−$\frac{1}{101}$)−($\frac{1}{103}$−$\frac{1}{102}$)−…−($\frac{1}{1000}$−$\frac{1}{999}$)
=$\frac{1}{100}$−$\frac{1}{101}$+$\frac{1}{101}$−$\frac{1}{102}$+$\frac{1}{102}$−$\frac{1}{103}$+…+$\frac{1}{999}$−$\frac{1}{1000}$
=$\frac{1}{100}$−$\frac{1}{1000}$
=$\frac{9}{1000}$.
(2)解:|$\frac{1}{101}$−$\frac{1}{100}$|+|$\frac{1}{102}$−$\frac{1}{101}$|+|$\frac{1}{103}$−$\frac{1}{102}$|+…+|$\frac{1}{1000}$−$\frac{1}{999}$|
=−($\frac{1}{101}$−$\frac{1}{100}$)−($\frac{1}{102}$−$\frac{1}{101}$)−($\frac{1}{103}$−$\frac{1}{102}$)−…−($\frac{1}{1000}$−$\frac{1}{999}$)
=$\frac{1}{100}$−$\frac{1}{101}$+$\frac{1}{101}$−$\frac{1}{102}$+$\frac{1}{102}$−$\frac{1}{103}$+…+$\frac{1}{999}$−$\frac{1}{1000}$
=$\frac{1}{100}$−$\frac{1}{1000}$
=$\frac{9}{1000}$.
2.【信息提取】在有些情况下,不需要计算出结果也能把绝对值符号去掉。
例如:|$\frac{1}{2} - 1$|$ = 1 - \frac{1}{2},$|$\frac{1}{3} - \frac{1}{2}$|$ = \frac{1}{2} - \frac{1}{3},$|$\frac{1}{4} - \frac{1}{3}$|$ = \frac{1}{3} - \frac{1}{4},……【$初步体验】(1)根据上面的规律,把下列式子写成去掉绝对值符号的形式(不要计算出结果):|$\frac{1}{19} - \frac{1}{18}$| =
例如:|$\frac{1}{2} - 1$|$ = 1 - \frac{1}{2},$|$\frac{1}{3} - \frac{1}{2}$|$ = \frac{1}{2} - \frac{1}{3},$|$\frac{1}{4} - \frac{1}{3}$|$ = \frac{1}{3} - \frac{1}{4},……【$初步体验】(1)根据上面的规律,把下列式子写成去掉绝对值符号的形式(不要计算出结果):|$\frac{1}{19} - \frac{1}{18}$| =
$\frac{1}{18}-\frac{1}{19}$
;【拓广应用】(2)计算|$\frac{1}{2} - 1$| + |$\frac{1}{3} - \frac{1}{2}$| + |$\frac{1}{4} - \frac{1}{3}$| + |$\frac{1}{5} - \frac{1}{4}$|;解:|$\frac{1}{2}$−1|+|$\frac{1}{3}$−$\frac{1}{2}$|+|$\frac{1}{4}$−$\frac{1}{3}$|+|$\frac{1}{5}$−$\frac{1}{4}$|
=1−$\frac{1}{2}$+$\frac{1}{2}$−$\frac{1}{3}$+$\frac{1}{3}$−$\frac{1}{4}$+$\frac{1}{4}$−$\frac{1}{5}$
=1−$\frac{1}{5}$
=$\frac{4}{5}$.
(3)计算|$\frac{1}{2} - 1$| + |$\frac{1}{3} - \frac{1}{2}$| + |$\frac{1}{4} - \frac{1}{3}$| + … + |$\frac{1}{2023} - \frac{1}{2022}$|。=1−$\frac{1}{2}$+$\frac{1}{2}$−$\frac{1}{3}$+$\frac{1}{3}$−$\frac{1}{4}$+$\frac{1}{4}$−$\frac{1}{5}$
=1−$\frac{1}{5}$
=$\frac{4}{5}$.
解:|$\frac{1}{2}$−1|+|$\frac{1}{3}$−$\frac{1}{2}$|+|$\frac{1}{4}$−$\frac{1}{3}$|+…+|$\frac{1}{2023}$−$\frac{1}{2022}$|
=1−$\frac{1}{2}$+$\frac{1}{2}$−$\frac{1}{3}$+$\frac{1}{3}$−$\frac{1}{4}$+…+$\frac{1}{2022}$−$\frac{1}{2023}$
=1−$\frac{1}{2023}$
=$\frac{2022}{2023}$.
=1−$\frac{1}{2}$+$\frac{1}{2}$−$\frac{1}{3}$+$\frac{1}{3}$−$\frac{1}{4}$+…+$\frac{1}{2022}$−$\frac{1}{2023}$
=1−$\frac{1}{2023}$
=$\frac{2022}{2023}$.
答案:2.(1)$\frac{1}{18}$−$\frac{1}{19}$
(2)解:|$\frac{1}{2}$−1|+|$\frac{1}{3}$−$\frac{1}{2}$|+|$\frac{1}{4}$−$\frac{1}{3}$|+|$\frac{1}{5}$−$\frac{1}{4}$|
=1−$\frac{1}{2}$+$\frac{1}{2}$−$\frac{1}{3}$+$\frac{1}{3}$−$\frac{1}{4}$+$\frac{1}{4}$−$\frac{1}{5}$
=1−$\frac{1}{5}$
=$\frac{4}{5}$.
(3)解:|$\frac{1}{2}$−1|+|$\frac{1}{3}$−$\frac{1}{2}$|+|$\frac{1}{4}$−$\frac{1}{3}$|+…+|$\frac{1}{2023}$−$\frac{1}{2022}$|
=1−$\frac{1}{2}$+$\frac{1}{2}$−$\frac{1}{3}$+$\frac{1}{3}$−$\frac{1}{4}$+…+$\frac{1}{2022}$−$\frac{1}{2023}$
=1−$\frac{1}{2023}$
=$\frac{2022}{2023}$.
(2)解:|$\frac{1}{2}$−1|+|$\frac{1}{3}$−$\frac{1}{2}$|+|$\frac{1}{4}$−$\frac{1}{3}$|+|$\frac{1}{5}$−$\frac{1}{4}$|
=1−$\frac{1}{2}$+$\frac{1}{2}$−$\frac{1}{3}$+$\frac{1}{3}$−$\frac{1}{4}$+$\frac{1}{4}$−$\frac{1}{5}$
=1−$\frac{1}{5}$
=$\frac{4}{5}$.
(3)解:|$\frac{1}{2}$−1|+|$\frac{1}{3}$−$\frac{1}{2}$|+|$\frac{1}{4}$−$\frac{1}{3}$|+…+|$\frac{1}{2023}$−$\frac{1}{2022}$|
=1−$\frac{1}{2}$+$\frac{1}{2}$−$\frac{1}{3}$+$\frac{1}{3}$−$\frac{1}{4}$+…+$\frac{1}{2022}$−$\frac{1}{2023}$
=1−$\frac{1}{2023}$
=$\frac{2022}{2023}$.