tana = 5/4
因为0＜a＜派/2
所以sina = 5√41/41,cosa = 4√41/41
所以cos2a + sin(a+派/2) = 2(cosa)^2 - 1 + cosa = 2*(4√41/41)^2 - 1 + 4√41/41 = (4√41 - 9)/41