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17. panjang kawat = 72 cm
misal AB = x
AC = y
cari hubungan x dan y:
x + y = 72 - 30
x + y = 42 → y = 42 - x
Lsegitiga = x.y/2 ; subtitusi y = 42 - x
L = x(42 - x)/2
L = 21x - (1/2)x² ; turunkan sekali
L' = 21 - x ; subtitusi L' = 0
0 = 21 - x
x = 21 cm
maka L = x(42 - x)/2
L = 21(42-21)/2
L = 21(21)/2
L = 220,5 cm²............opsi C