求值:sin10sin30sin50sin70
1个回答

sin10sin30sin50sin70 =

1/2 * sin10 * sin50 * sin70 =

1/2 * sin10 * cos20 * cos 40 =

1/2 * cos10 * sin10 * cos20 * cos 40 / cos10 =

1/4 * sin20 * cos20 * cos40 / cos10 =

1/8 * sin40 * cos40 / cos10 =

1/16 * sin80 / cos10 =

1/16 * cos10 / cos10 =

1/16