Jawaban:

Cara 1

Luas lingkaran:

table attributes columnalign right center left columnspacing 0px end attributes row straight L equals cell πr squared end cell row cell 1.256 end cell equals cell 3 comma 14 cross times straight r squared end cell row cell 1.256 divided by 3 comma 14 end cell equals cell straight r squared end cell row cell straight r squared end cell equals 400 row cell square root of straight r squared end root end cell equals cell plus-or-minus square root of 400 end cell row straight r equals cell plus-or-minus 20 end cell end table

karena jari-jari adalah satuan jarak, jadi kita gunakan r = 20 cm.

Diameter lingkaran:

begin mathsize 14px style text d=2r=2×20=40 end text end style

Cara 2

Luas lingkaran:

table attributes columnalign right center left columnspacing 0px end attributes row straight L equals cell 1 fourth πd squared end cell row cell 1.256 end cell equals cell 1 fourth cross times 3 comma 14 cross times straight d squared end cell row cell 1.256 cross times 4 end cell equals cell 3 comma 14 cross times straight d squared end cell row cell 5.024 end cell equals cell 3 comma 14 cross times straight d squared end cell row cell straight d squared end cell equals cell 5.024 divided by 3 comma 14 end cell row cell square root of straight d squared end root end cell equals cell plus-or-minus square root of 1.600 end root end cell row straight d equals cell plus-or-minus 40 end cell end table

karena diameter adalah satuan jarak, jadi kita gunakan d = 40 cm.

Jadi, diameter lingkaran tersebut begin mathsize 14px style text 40 cm end text end style.