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P=πr²
Oblicz pole koła o obwodzie:
a)2πr=16π /:2
πr=8π/:π
r=8
P = π * 8² = 64π (cm²)
b)2πr=π |:2
πr=½ π |:π
r=π / 2π
r=½
P=¼π (m²)
c)2πr=0,12π |:2
πr=0,06π |:π
r=0,06
P=0,0036π (mm²)
d)2πr=⅔π /:2
πr=2/6π /:π
r=1/3
P=(1/3)² * π = 1/9π (km²)
e)2πr=4 /:2
πr=2 /:π
r=2 / π
P=π * ( 2/π)² = π * 4/π = π * 16/π² = 16/π (dm²)
Oblicz obwód koła o polu:
a) πr²=16π /:π
r²=16
r=4
Obw=2*4*π=8π (cm)
b)πr²=⁴/₉π /:π
r²=4/9
r=2/3
Obw=2*2/3*π=4/3π (m)
πr²=0,25π/:π
r²=0,25
r=0,5
Obw=2πr
Obw=2*0,5*π=π (mm)
πr²=2π /:π
r²=2
r=√2
Obw=2*√2*π=2π√2 (dm)
πr²=3/:π
r²=3/π
r=√(3/π)
Obw = 2 * π * √(3/π) =2√3π (km)