15°cos7° - cos11°cos79°
= 15(cos7°) - (cos11°)(cos79°)≈ 15(0.990) - (0.990)(0.173)
= 14.85 - 0.17127≈ 14.67873
15°cos7° - cos11°cos79°
= 15(cos7°) - (cos11°)(cos79°)
≈ 15(0.990) - (0.990)(0.173)
= 14.85 - 0.17127
≈ 14.67873