উত্তর সিলেক্ট করলে সঠিক ও ভুল দেখাবে।
ব্যাখ্যা ও সঠিক সমাধান
উত্তর:
2acos(B-C)/2
b + c = 2R sinB + 2R sinC = 2R(sinB + sinC) = 2R(2sin(B+C)/2 cos(B-C)/2) = 2R(2sin(180-A)/2 cos(B-C)/2) = 2R(2sin(90-A/2) cos(B-C)/2) = 4R cos(A/2) cos(B-C)/2 = 4R cos(30°) cos(B-C)/2 = 4R(√3/2) cos(B-C)/2 = 2R√3 cos(B-C)/2. Since a = 2R sinA = 2R sin60° = 2R(√3/2) = R√3, then b+c = 2acos(B-C)/2.