式子cos9°-sin9°/sin18°cos18

式子cos9°-sin9°/sin18°cos18°的值是?

1个回答

(cos9°－sin9°)/(sin18°cos18°)
=[√2cos(9°＋45°)]/[(1/2)sin(2×18°)]
=2√2(cos54°)/(sin36°)
=2√2cos54°/cos54°
=2√2