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5. ditanya volume setengah tabung
   r = 42 : 2 = 21
 tinggi tabung = 90 cm

  volume tabung = π x r² x t
  volume setengah tabung = 1/2 x π × r² x t
                                          = 1/2 x 22/7 x 21 x 21 x 90
                                          = 22/14 x 21 x 21 x 90
                                          = 33 x 21 x 90
                                          = 62.370 cm³

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