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Misal
sisi Belah Ketupat = x


x*2 = 9*2 + 12*2
x*2 = 81 + 144
x*2 = 225
x = √225
x = 15 cm
Keliling = 8 ( 15 ) + 2(9)
= 120 + 18
= 138 cm

Jawaban = d. 138