连续函数的极限值等于该点处的函数值.
1.原式= 0 / tan1 = 0
2.原式= lim(x->π/2) ( 1+ cos3x) ^ secx （1+o）^ ∞
= e^ lim(x->π/2) secx ln( 1+ cos3x)
= e^ lim(x->π/2) ln( 1+ cos3x) / cosx
= e^ lim(x->π/2) cos3x / cosx 等价无穷小代换：ln(1+cos3x) cos3x
= e^ lim(x->π/2) ﹣3 sin3x / (﹣sinx) 洛必达法则
= e^(﹣3)