計(jì)算題:
(1)-24÷(-14)×(-7);
(2)3×(-9)-(-15)×(-3)-3×18;
(3)(5a2-3b2)-[(a2-2ab-b2)-(5a2-2ab-3b2)];
分析:(1)先算乘方,再把除法變?yōu)槌朔ㄓ?jì)算即可;
(2)根據(jù)乘法的分配律的逆運(yùn)算,可以簡(jiǎn)化計(jì)算;
(3)先去小括號(hào),再去中括號(hào),最后合并同類項(xiàng).
解答:解:(1)-2
4÷(-14)×(-7)=-16×(-
)×(-7)=-8;
(2)3×(-9)-(-15)×(-3)-3×18
=3×(-9-15-18)
=3×(-42)
=-126;
(3)(5a
2-3b
2)-[(a
2-2ab-b
2)-(5a
2-2ab-3b
2)]
=5a
2-3b
2-[a
2-2ab-b
2-5a
2+2ab+3b
2]
=5a
2-3b
2-a
2+2ab+b
2+5a
2-2ab-3b
2
=9a
2-5b
2.
點(diǎn)評(píng):(1)解決整式加減混合運(yùn)算的關(guān)鍵是熟記去括號(hào)法則,熟練運(yùn)用合并同類項(xiàng)的法則,這是各地中考的�?键c(diǎn).
(2)有理數(shù)混合運(yùn)算的順序,有括號(hào)先算括號(hào)里面的,再按照先乘方,后乘除,最后算加減的順序進(jìn)行計(jì)算.注意運(yùn)用運(yùn)算律簡(jiǎn)化計(jì)算.