《2025年天天练口算六年级数学上册人教版》

求下面各圆的周长
$ r = 2.4\ \text{dm} $
$ r = 1\ \text{m} $
$ d = 10\ \text{cm} $

答案： 1. $ C = 2\pi r = 2×3.14×2.4 = 15.072\ \text{dm} $
2. $ C = 2\pi r = 2×3.14×1 = 6.28\ \text{m} $
3. $ C = \pi d = 3.14×10 = 31.4\ \text{cm} $
4. $ C = 2\pi r = 2×3.14×7 = 43.96\ \text{cm} $
5. $ C = \pi d = 3.14×20 = 62.8\ \text{cm} $
6. $ C = \pi d = 3.14×16 = 50.24\ \text{cm} $

$ 3.14×1= $3.14
$ 3.14×2= $6.28
$ 3.14×3= $9.42
$ 3.14×4= $12.56
$ 3.14×5= $15.7
$ 3.14×6= $18.84
$ 3.14×7= $21.98
$ 3.14×8= $25.12
$ 3.14×9= $28.26
$ 3.14×10= $31.4
$ 3.14×50= $157
$ 3.14×60= $188.4
$ 3.14×500= $1570
$ 3.14×600= $1884
$ 3.14×0.5= $1.57
$ 3.14×0.6= $1.884
$ 3.14×40= $125.6
$ 3.14×20= $62.8
$ 3.14×0.2= $0.628
$ 3.14×15= $47.1

答案： $3.14×1 = 3.14$
$3.14×2 = 6.28$
$3.14×3 = 9.42$
$3.14×4 = 12.56$
$3.14×5 = 15.7$
$3.14×6 = 18.84$
$3.14×7 = 21.98$
$3.14×8 = 25.12$
$3.14×9 = 28.26$
$3.14×10 = 31.4$
$3.14×50 = 157$
$3.14×60 = 188.4$
$3.14×500 = 1570$
$3.14×600 = 1884$
$3.14×0.5 = 1.57$
$3.14×0.6 = 1.884$
$3.14×40 = 125.6$
$3.14×20 = 62.8$
$3.14×0.2 = 0.628$
$3.14×15 = 47.1$