有理数乘法、除法、乘方、科学计数法、有效数字与近似
数、混合运算知识点
一、有理数的乘法
(1)有理数乘法法则:两数相乘，同号得正，异号得负，并把绝对值相乘( (2)任何数同零相乘，都得0(
(3)多个有理数相乘的法则:?几个不等于0的数相乘，积的符号由负因数的个数决定，当负因数有奇数个时，积为负;当负因数有偶数个时，积为正(?几个数相乘，有一个因数为0，积就为0(
(4)方法指引:
?运用乘法法则，先确定符号，再把绝对值相乘(
?多个因数相乘，看0因数和积的符号当先，这样做使运算既准确又简单( Eg:计算3×(-3)的结果是( )
A、6 B、-6 C、9 D、-9
Eg:计算(-6)×(-1)的结果等于( ) A、6 B、-6 C、1 D、-1 二、倒数
(1)倒数:乘积是1的两数互为倒数(
11一般地，a?=1 (a?0)，就说a(a?0)的倒数是( aa (2)方法指引:
?倒数是除法运算与乘法运算转化的“桥梁”和“渡船”(正像减法转化为加法及相反数一样，非常重要(倒数是伴随着除法运算而产生的( ?正数的倒数是正数，负数的倒数是负数，而0 没有倒数，这与相反数不同( Eg:-2的倒数是( )
11
22 A、2 B、-0.2 C、 D、- 三、有理数的除法
(1)有理数除法法则:除以一个不等于0的数，等于乘这个数的倒数，即: 1a?b=a? (b?0) b (2)方法指引:
(1)两数相除，同号得正，异号得负，并把绝对值相除(0除以任何一个不等于0的数，都得0(
along the ridge line on the plane, and nearly vertical slope contour lines, Guan Po changes with the original ground line, with shallow backfill-pipe, single-pipe water supply, the competent 1.4m, long 1063.506m, two asymmetric \to establish 12 town Pier, 8 expansion joint. Town pier for the closed-end structure of gravity, placed on soft rock base surface, pipe concrete C20 on a pedestal. Pipe trench excavation slope 1:0.75, after the installation of steel tube, compacted gravel backfill material to the surface, and 1:100 slope drainage to gutters. Gutter width 0.5M depth 0.5m,M5 grouted rubble masonry. 9.2 main engineering content this standard pressure pipe and the metal structure installation part main including Yunnan province tengchong County yongxing River primary and secondary hydropower station in the of pressure pipe and the power station metal structure, which level power station pressure pipe total about 562t (containing annex); II level power station pressure pipe about 733 t (containing