Jika luas ∆ABC adalah 54 cm^2 , keliling ∆ABC adalah ....
Luas ΔABC = 1/2 x alas x tinggi
54 = 1/2 X 12 X (x + 3)
54 = 6 X (x + 3)
(x + 3) = 54/6
x + 3 = 9
x = 9 - 3
x = 6
AC = x + 3
AC = 6 + 3
AC = 9 cm
BC² = AB² + AC²
BC² = 12² + 9²
BC² = 144 + 81
BC² = 225
BC = √225
BC = 15 cm
Keliling ΔABC = AB + BC + AC
Keliling ΔABC = 12 + 15 + 9
Keliling ΔABC = 36 cm
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