∫cos^2xdx
=1/2∫1+cos2xdx
=1/2(x+∫cos2xdx)
=1/2(x+1/2∫dsin2x)
=x/2+sin2x/4+C
f(x)=e^x/a+a/e^x
f(-x)=e^(-x)/a+a/e^(-x)=1/(ae^x)+ae^x
偶函数则f(x)=f(-x)
e^x/a+a/e^x=1/(ae^x)+ae^x
即e^x/a+a/e^x=ae^x+1/(ae^x)
所以1/a=a
a>0
a=1
原式=∫(1+cos2x)/2 dx
=1/4∫(1+cos2x)d(2x)
=(2x+sin2x)/4+C