[(1+cos20°)/2sin20°]-sin10°(1/tan5°-tan5°)
=[(1+cos20°)/2sin20°]- sin10°(cot5°-tan5°)
=[(1+cos20°)/4sin10°cos10°]-sin10°(cot5°-tan5°)
=(2cos10 °/4sin10°)-2sin5°cos5°(cot5°-tan5°)
=(cos10°/2sin10°)-2((cos5°)＾2-(sin5°)＾2) < /p>
=(cos10°/2sin10°)-2cos10°
=(cos10°-4sin10°cos10°)/2sin10°
=(sin80°-2sin20 °)/2sin10°
=((sin80°-sin20°)-sin20°)/2sin10°
=(2cos50°sin30°-sin20°)/2sin10°
=(sin40°-sin20°)/2sin10°
={2cos30°sin10°)/2sin10°
=cos30°
= (root 3)/2