计算题.2.21,28,33,42,43,60,( ) A.45 B.56 C.75 D.92 这题怎么算啊,计算题.2.21,28,33,42,43,60,( )A.45 B.56 C.75 D.92这题怎么算啊,
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![计算题.2.21,28,33,42,43,60,( ) A.45 B.56 C.75 D.92 这题怎么算啊,计算题.2.21,28,33,42,43,60,( )A.45 B.56 C.75 D.92这题怎么算啊,](/uploads/image/z/37114-34-4.jpg?t=%E8%AE%A1%E7%AE%97%E9%A2%98.2%EF%BC%8E21%2C28%2C33%2C42%2C43%2C60%2C%EF%BC%88+%EF%BC%89+A%EF%BC%8E45+B%EF%BC%8E56+C%EF%BC%8E75+D%EF%BC%8E92+%E8%BF%99%E9%A2%98%E6%80%8E%E4%B9%88%E7%AE%97%E5%95%8A%2C%E8%AE%A1%E7%AE%97%E9%A2%98.2%EF%BC%8E21%2C28%2C33%2C42%2C43%2C60%2C%EF%BC%88+%EF%BC%89A%EF%BC%8E45+B%EF%BC%8E56+C%EF%BC%8E75+D%EF%BC%8E92%E8%BF%99%E9%A2%98%E6%80%8E%E4%B9%88%E7%AE%97%E5%95%8A%2C)
计算题.2.21,28,33,42,43,60,( ) A.45 B.56 C.75 D.92 这题怎么算啊,计算题.2.21,28,33,42,43,60,( )A.45 B.56 C.75 D.92这题怎么算啊,
计算题.2.21,28,33,42,43,60,( ) A.45 B.56 C.75 D.92 这题怎么算啊,
计算题.
2.21,28,33,42,43,60,( )
A.45 B.56 C.75 D.92
这题怎么算啊,
计算题.2.21,28,33,42,43,60,( ) A.45 B.56 C.75 D.92 这题怎么算啊,计算题.2.21,28,33,42,43,60,( )A.45 B.56 C.75 D.92这题怎么算啊,
A.45
21 28 33 42 43 60 ( 45 )
+7 + 5 +9 +1 +17 ( -15)
-2 +4 -8 +16 (-32)
选A,做两次差
21 28 33 42 43 60 45
7 5 9 1 17 -15
2 -4 8 -16 然后反过来推 32
45。
后项减前项作差得:7,5,9,1,17
再作差得:-2,4,-8,16
得公比为2的等差数列。
所以16后面是-32
所以17后面是17-32=-15
60+(-15)=45
选A,21+7=28,28+5=33,,33+9=42,42+1=43,43+17=60,60-15=45
为什么33+9,因为,7+(7-5)=9,为什么42+1,因为5+(5-9)=1,为什么43+17,因为9+(9-1)=17
为什么60-15,因为1+(1-17)=-15,
45
做极差7 5 9 1 17 (-15)
-2 4 -8 16 (-32)