解:(1)25.3+(-7.3)-(-13.7)+7.3
=25.3-(13.7)+[(-7.3)+7.3]
=25.3+13.7
=39;
(2)(1
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-
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+
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)×(-24)
=
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×(-24)+(-
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)×(-24)+
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×(-24)
=(-36)+9+(-14)
=(-50)+9
=-(50-9)
=-41;
(3)
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=
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×(-9×
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-
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)×(-
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)
=
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×(-
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)×(-
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)
=1.
分析:(1)利用加法運算律把-7.3與7.3結(jié)合,根據(jù)互為相反數(shù)的兩數(shù)之和為0計算,把剩下的兩項利用減去一個數(shù)等于加上這個數(shù)的相反數(shù)把減法運算化為加法運算,即可求出結(jié)果;
(2)利用乘法分配律給括號中每一項都乘以-24,利用兩數(shù)相乘同號得正、異號得負,并把絕對值相乘的法則計算,約分后把各種的積相加,即可得到最后結(jié)果;
(3)根據(jù)運算順序,先算乘方運算,-3
2表示兩個3乘積的相反數(shù),(-
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)
2表示兩個-
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的乘積,利用減法法則計算中括號中的式子得出結(jié)果,然后利用除以一個數(shù)等于乘以這個數(shù)的倒數(shù)把除法運算化為乘法運算,約分后即可得到最后結(jié)果.
點評:此題考查了有理數(shù)的混合運算,有理數(shù)的混合運算首先弄清運算順序,先乘方,再乘除,最后算加減,有括號先算括號里邊的,同級運算從左到右依次計算,然后利用各種運算法則來計算,有時可以利用運算律來簡化運算,比如第二小題,注意-3
2與(-3)
2的區(qū)別,前者表示3平方的相反數(shù),后者表示兩個-3的乘積.