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<p>∠RPQ + ∠RQP + ∠QRP = 180°</p><p>30° + 45° + ∠QRP = 180°</p><p>75° + ∠QRP = 180°</p><p>∠QRP = 180° - 75°</p><p>∠QRP = 105°</p><p>&nbsp;</p><p>Gunakan <i>Aturan Sinus</i> :</p><p>a. PQ/Sin R = RP/Sin Q</p><p>15/Sin 105° = RP/Sin 45°</p><p>15/(Sin (60° + 45°)) = RP/(½√2)</p><p>15/(Sin 60° Cos 45° + Cos 60° Sin 45°) = 2RP/(√2)</p><p>15/((½√3)(½√2) + (½)(½√2)) = ((2√2)RP)/2</p><p>15/((√6 + √2)/4) = √2RP</p><p>15/1 × 4/(√6 + √2) = √2RP</p><p>60/(√6 + √2) = √2RP</p><p>(60(√6 - √2))/4 = √2RP</p><p>15(√6 - √2) = √2RP</p><p>15√6 - 15√2 = RP</p><p>15√3 - 15 = RP</p><p>RP ≈ 10,98 m.</p><p>&nbsp;</p><p>b. PQ/Sin R = QR/Sin P</p><p>15(√6 - √2) = QR/Sin 30°</p><p>15(√6 - √2) = QR/(½)</p><p>15√6 - 15√2 = 2QR</p><p>QR = (15√6 - 15√2)/2 ≈ 7,76 m.</p><p>&nbsp;</p><p>c. Luas segitiga PQR :</p><p>L = √(S(S - p)(S - q)(S - r))</p><p>S = ½(p + q + r)</p><p>S = ½(7,76 + 10,98 + 15)</p><p>S = ½(33,74)</p><p>S = 16,87</p><p>&nbsp;</p><p>L = √(S(S - p)(S - q)(S - r))</p><p>L = √((16,87)(16,87 - 7,76)(16,87 - 10,98)(16,87 - 15)) ≈ 155,96 m²</p><p>&nbsp;</p><p>Luas segitiga I = luas segitiga II</p><p>155,96 = ½ × PQ × lebar sungai</p><p>½ × 15 × lebar = 155,96</p><p>7,5 × lebar = 155,96</p><p>Lebar = 155,96/7,5</p><p>Lebar sungai = 20,79 m.</p><p>&nbsp;</p><p>Semoga membantu.</p>