Question

一道初中数学题，在线等、、、、急!

已知一个圆的周长是62.8，求它的半径？？？有公式吗？？谢谢解答。求详细。

Answer 1

周长=圆的直径×3.14（π）=2*圆的半径×3.14 62.8除3.14除2就是半径了

Answer 2

微积分公式
Dx sin x=cos x
cos x = -sin x
tan x = sec2 x
cot x = -csc2 x
sec x = sec x tan x
csc x = -csc x cot x
sin x dx = -cos x + C
cos x dx = sin x + C
tan x dx = ln |sec x | + C
cot x dx = ln |sin x | + C
sec x dx = ln |sec x + tan x | + C
csc x dx = ln |csc x - cot x | + C
sin-1(-x) = -sin-1 x
cos-1(-x) = - cos-1 x
tan-1(-x) = -tan-1 x
cot-1(-x) = - cot-1 x
sec-1(-x) = - sec-1 x
csc-1(-x) = - csc-1 x
Dx sin-1 ()=
cos-1 ()=
tan-1 ()=
cot-1 ()=
sec-1 ()=
csc-1 (x/a)=
sin-1 x dx = x sin-1 x++C
cos-1 x dx = x cos-1 x-+C
tan-1 x dx = x tan-1 x- ln (1+x2)+C
cot-1 x dx = x cot-1 x+ ln (1+x2)+C
sec-1 x dx = x sec-1 x- ln |x+|+C
csc-1 x dx = x csc-1 x+ ln |x+|+C
sinh-1 ()= ln (x+) xR
cosh-1 ()=ln (x+) x≥1
tanh-1 ()=ln () |x| 1
sech-1()=ln(+)0≤x≤1
csch-1 ()=ln(+) |x| >0
Dx sinh x = cosh x
cosh x = sinh x
tanh x = sech2 x
coth x = -csch2 x
sech x = -sech x tanh x
csch x = -csch x coth x
sinh x dx = cosh x + C
cosh x dx = sinh x + C
tanh x dx = ln | cosh x |+ C
coth x dx = ln | sinh x | + C
sech x dx = -2tan-1 (e-x) + C
csch x dx = 2 ln || + C
duv = udv + vdu
duv = uv = udv + vdu
→ udv = uv - vdu
cos2θ-sin2θ=cos2θ
cos2θ+ sin2θ=1
cosh2θ-sinh2θ=1
cosh2θ+sinh2θ=cosh2θ
Dx sinh-1()=
cosh-1()=
tanh-1()=
coth-1()=
sech-1()=
csch-1(x/a)=
sinh-1 x dx = x sinh-1 x-+ C
cosh-1 x dx = x cosh-1 x-+ C
tanh-1 x dx = x tanh-1 x+ ln | 1-x2|+ C
coth-1 x dx = x coth-1 x- ln | 1-x2|+ C
sech-1 x dx = x sech-1 x- sin-1 x + C
csch-1 x dx = x csch-1 x+ sinh-1 x + C
sin 3θ=3sinθ-4sin3θ
cos3θ=4cos3θ-3cosθ
→sin3θ= (3sinθ-sin3θ)
→cos3θ= (3cosθ+cos3θ)
sin x = cos x =
sinh x = cosh x =
正弦定理:= ==2R
余弦定理: a2=b2+c2-2bc cosα
b2=a2+c2-2ac cosβ
c2=a2+b2-2ab cosγ
sin (α±β)=sin α cos β ± cos α sin β
cos (α±β)=cos α cos β sin α sin β
2 sin α cos β = sin (α+β) + sin (α-β)
2 cos α sin β = sin (α+β) - sin (α-β)
2 cos α cos β = cos (α-β) + cos (α+β)
2 sin α sin β = cos (α-β) - cos (α+β)
sin α + sin β = 2 sin (α+β) cos (α-β)
sin α - sin β = 2 cos (α+β) sin (α-β)
cos α + cos β = 2 cos (α+β) cos (α-β)
cos α - cos β = -2 sin (α+β) sin (α-β)
tan (α±β)=, cot (α±β)=
ex=1+x+++…++ …
sin x = x-+-+…++ …
cos x = 1-+-+++
ln (1+x) = x-+-+++
tan-1 x = x-+-+++
(1+x)r =1+rx+x2+x3+ -1= n
= n (n+1)
= n (n+1)(2n+1)
= [ n (n+1)]2
Γ(x) = x-1e-t dt = 22x-1dt = x-1 dt
β(m, n) =m-1(1-x)n-1 dx=22m-1x cos2n-1x dx = dx

Answer 3

周长等于直径乘以圆周率，你反推一下就成了

Answer 4

周长公式是
2πr
即62.8÷(2×3.14）=10

追问

为什么周长公式是2πr???/、

Answer 5

C=2πr C=62.8 π=3.14 所以r=10