由于mathematica 失效，无法给出a的值，特此求助，请给出a的值的度数

tga=
-2.47738282846
-4.95476565692
-7.432148485380001
-9.90953131384
-12.3869141423
-14.86429697076
-17.34167979922
-19.81906262768
-22.29644545614
-24.7738282846
-27.25121111306
-29.72859394152001
-32.20597676998001
-34.68335959844
-37.1607424269
-39.63812525536
-42.11550808382001
-44.59289091228001
-47.07027374074
-49.5476565692
-52.02503939766
-54.50242222612001
-56.97980505458
-59.45718788304001
-61.9345707115
-64.41195353996001
-66.88933636842
-69.36671919688
-71.84410202534001
-74.3214848538
-76.79886768226001
-79.27625051072
-81.75363333918
-84.23101616764001
-86.7083989961
-89.18578182456001
-91.66316465302
-94.14054748148
-96.61793030994001
-99.0953131384
-101.57269596686
-104.05007879532
-106.52746162378
-109.00484445224
-111.4822272807
-113.95961010916
-116.43699293762
-118.91437576608
-121.39175859454
-123.869141423
-126.34652425146
-128.82390707992