Tanpa menggunakan tabel trigonometri maupun kalkulator, hitung: sin² 6° + sin² 42° + sin² 66° + sin² 78° = ...

→Sin²6° + sin²42° + Sin²66° + Sin²78°
=[Sin²66 + sin²6] +
[ sin²78+sin²42]
=[2sin²½(66+6)cos²½(66-6)] + [2sin²½(78+42)cos²½(78-42)]
=[2sin²36°cos²30° ] + [2sin²60°cos²36°]
= 2sin²36° (½√3)² + 2(½√3)cos²(36)°
= 2sin²36°(3/4)+ 2(3/4)cos²(36)°
= (3/2)sin²36°+ (3/2)cos²(36)°
= (3/2)( sin²36° + cos²36°)
= (3/2)(1)
=3/2
jadi hasil akhirnya 3/2