f( x)= sin( wx+ a)+ cos( wx+ a)=根号2[cosπ/4 *sin( wx+ a)+sinπ/4cos( wx+ a)]==根号2sin(wx+ a+π/4 ) 两相邻对称轴之间的距离为π/2 T=2*π/2=π
w=2π/T=2 f( x)= f(- x) f(x)为偶函数
f(x)=根号2cos(2x)