问题
填空题
已知数列{an}为等差数列,且a1+a8+a15=π,a=cos (a4+a12),则 xadx=________.
答案
2
∵a1+a8+a15=π,∴a8=,∴a=cos (a4+a12)=cos (2a8)=cos
=-
,
∴xadx=
=2.
已知数列{an}为等差数列,且a1+a8+a15=π,a=cos (a4+a12),则 xadx=________.
2
∵a1+a8+a15=π,∴a8=,∴a=cos (a4+a12)=cos (2a8)=cos
=-
,
∴xadx=
=2.