COS(2A-π/4) = COS2A COSπ/4+SIN2ASINπ/4
=√2∕2〔COS2A+SIN2A〕
COS2A =2*(cosX)^2-1=-7∕25
SIN2A=2COSASINA=24∕25
1+根2COS(2A-π/4) =42∕25
SIN(A+π/2)= COSA =3/5
原式=14∕5