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電子課本網(wǎng) 第48頁

第48頁

信息發(fā)布者:
?$ \begin{aligned} 解:原式&=7+2-3 \\ &=6 \\ \end{aligned}$?
?$ \begin{aligned} 解:原式&=-(\frac {2}{3}+\frac {1}{3})+(2\frac {4}{7}+\frac {5}{7}) \\ &=(-1)+3\frac {2}{7} \\ &=2\frac {2}{7} \\ \end{aligned}$?
?$ \begin{aligned} 解:原式&=81×\frac {4}{9}×\frac {4}{9}×\frac {1}{2} \\ &=16×\frac {1}{2} \\ &=8 \\ \end{aligned}$?
?$ \begin{aligned} 解:原式&=2×9+8+10 \\ &=18+8+10 \\ &=36 \\ \end{aligned}$?
?$ 解:(1)原式=6×\frac {1}{6}-4$?
?$=1-4$?
?$=-3$?
?$(2)設(shè)被污染的數(shù)字為x,則6×(\frac {2}{3}-x)-22=0$?
?$則6×(\frac {2}{3}-x)=4$?
?$\frac {2}{3}-x=\frac {2}{3}$?
?$x=0,被污染的數(shù)字是0$?
?$ \begin{aligned} 解:原式&=(-28)+\frac {3}{4}×4 \\ &=(-28)+3 \\ &=-25 \\ \end{aligned}$?
?$ 解:原式=(-1)-\frac {1}{2}×\frac {1}{4}×(4+1)$?
?$=(-1)-\frac {1}{8}×5$?
?$=(-1)-\frac {5}{8}$?
?$=-1\frac {5}{8}$?
?$ \begin{aligned} 解:原式&=(-36-64)÷(-6+8) \\ &=(-100)÷2 \\ &=-50 \\ \end{aligned}$?
?$ 解:原式=(100-\frac {1}{5})×(-5)-(99+\frac {1}{3})×(-9)$?
?$=(-500)+1-(-891-3)$?
?$=-500+1+891+3$?
?$=395$?
?$ 解:由題意:a=±3,b=±5,因為a>b,所以分兩種情況$?
?$①a=3,b=-5$?
?$此時b-2a=(-5)-2×3=-11$?
?$②a=-3,b=-5$?
?$此時b-2a=(-5)-2×(-3)=1$?
?$則b-2a的值為1或-11$?