兩題中五數學問題

1)
sin^2 400° +cos^2 220°+tan^2 315°
=sin^2 (360°+40°) +cos^2 (180°+40°)+tan^2 (360°-45°)
=sin^2 40° +cos^2 40°+tan^2 45°
=1+1
=2
2)
1/(2√3+ √2)
=1/(2√3+ √2)*[(2√3- √2)/(2√3- √2)]
=(2√3- √2)/10 [用 (a-b)(a+b)=a^2-b^2]
=√2(√6- 1)/10