Tentukan jari-jari lingkaran

Tentukan jari-jari lingkaran

Tentukan jari-jari lingkaran

Jawaban : 3 cm

Ingat : pada ∆PQR dengan sudut Q adalah 90°, berlaku teorema Pythagoras :
PR² = QR²+PQ²
Luas ∆ = ½×alas×tinggi
Jari-jari lingkaran dalam segitiga : r= L∆/S
Dimana L∆= luas segitiga
S = ½ dari keliling = ½(PQ+QR+PR)

Sehingga,
PR² = QR²+PQ²
PR² = 9²+12²
PR² = 81+144
PR² = 225
PR = ±√225
PR = ±15(karena ukuran panjang, ambil nilai positif)
PR = 15

Luas ∆ = ½×alas×tinggi
Luas ∆ = ½×9×12
Luas ∆ = 54

S= ½×(keliling lingkaran)
S= ½(9+12+15)
S= ½(36)
S= 18

r = L∆/S
r = 54/18
r = 3 cn

Jadi, panjang jari-jarinya adalah 3 cm

Semoga membantu ya

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