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sin ( x+45) = b/1
misal 2x+60 = A dan x+45 = B
sin A = a/1 dan sin B = b/1
sin(A+B) = sin (3x+105)
sin(A-B) = sin (x+15)
sin(A+B).sin(A-B) = sin (3x+105).sin (x+15)
ingat rumus penjumlahan dua sudut utk sinus
[sinAcosB+cosAsinB ][sinAcosB-cosAsinB]
cari dulu cosA dan cosB
sin A = a/1 gunakan segitiga siku2 sisi sampingnya
cosA = √1-a²
dan sin B = b/1
caranya sama cosB = √1-b²
[sinAcosB+cosAsinB ][sinAcosB-cosAsinB]=
sin²Acos²B-cos²Asin²B= a²(1-b²) - (1-a²)b² = a²-a²b²-b²+a²b² = a²-b²
jawaban A