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11..
K = 15 + 12 + 8
K = 35 cm

12.
Segitiga sama sisi
K = 3S
K = 3(23)
K = 69 cm

13.
K = 20 + 12 + x
40 = 32 + x
40 - 32 = x
8 = x

Jadi x = 8 cm

14.
Panjang sisi = 25 cm

Maka
K = 3S
K = 3(25)
K = 75 cm

Bangun Datar

Keliling segitiga = jumlah seluruh sisi

11) K segitiga = 8 + 15 + 12 = 35 cm

12) K segitiga = 23 x 3 = 69 cm

13) K segitiga = X + 20 + 12
40 = X + 32
X = 40 - 32
X = 8 cm

14) K segitiga = 25 x 3 = 75 cm

15) L segitiga = 1/2 x alas x tinggi
= 1/2 x 20 x 21
= 10 x 21
= 210 dm

*semoga membantu. sukses selalu ^_^