atan

<?

$num = tan(deg2rad(360));

$return = atan($num);

echo $return;

-2.4492935982947E-16

<?

for($i = 0; $i <= 360; ++$i)
{
    $num = tan(deg2rad($i));

    $return = atan($num);

    echo "$i: $return" . PHP_EOL;
}

0: 0
1: 0.017453292519943
2: 0.034906585039887
3: 0.05235987755983
4: 0.069813170079773
5: 0.087266462599716
6: 0.10471975511966
7: 0.1221730476396
8: 0.13962634015955
9: 0.15707963267949
10: 0.17453292519943
11: 0.19198621771938
12: 0.20943951023932
13: 0.22689280275926
14: 0.24434609527921
15: 0.26179938779915
16: 0.27925268031909
17: 0.29670597283904
18: 0.31415926535898
19: 0.33161255787892
20: 0.34906585039887
21: 0.36651914291881
22: 0.38397243543875
23: 0.4014257279587
24: 0.41887902047864
25: 0.43633231299858
26: 0.45378560551853
27: 0.47123889803847
28: 0.48869219055841
29: 0.50614548307836
30: 0.5235987755983
31: 0.54105206811824
32: 0.55850536063819
33: 0.57595865315813
34: 0.59341194567807
35: 0.61086523819802
36: 0.62831853071796
37: 0.6457718232379
38: 0.66322511575785
39: 0.68067840827779
40: 0.69813170079773
41: 0.71558499331768
42: 0.73303828583762
43: 0.75049157835756
44: 0.7679448708775
45: 0.78539816339745
46: 0.80285145591739
47: 0.82030474843733
48: 0.83775804095728
49: 0.85521133347722
50: 0.87266462599716
51: 0.89011791851711
52: 0.90757121103705
53: 0.92502450355699
54: 0.94247779607694
55: 0.95993108859688
56: 0.97738438111682
57: 0.99483767363677
58: 1.0122909661567
59: 1.0297442586767
60: 1.0471975511966
61: 1.0646508437165
62: 1.0821041362365
63: 1.0995574287564
64: 1.1170107212764
65: 1.1344640137963
66: 1.1519173063163
67: 1.1693705988362
68: 1.1868238913561
69: 1.2042771838761
70: 1.221730476396
71: 1.239183768916
72: 1.2566370614359
73: 1.2740903539559
74: 1.2915436464758
75: 1.3089969389957
76: 1.3264502315157
77: 1.3439035240356
78: 1.3613568165556
79: 1.3788101090755
80: 1.3962634015955
81: 1.4137166941154
82: 1.4311699866354
83: 1.4486232791553
84: 1.4660765716752
85: 1.4835298641952
86: 1.5009831567151
87: 1.5184364492351
88: 1.535889741755
89: 1.553343034275
90: 1.5707963267949
91: -1.553343034275
92: -1.535889741755
93: -1.5184364492351
94: -1.5009831567151
95: -1.4835298641952
96: -1.4660765716752
97: -1.4486232791553
98: -1.4311699866354
99: -1.4137166941154
100: -1.3962634015955
101: -1.3788101090755
102: -1.3613568165556
103: -1.3439035240356
104: -1.3264502315157
105: -1.3089969389957
106: -1.2915436464758
107: -1.2740903539559
108: -1.2566370614359
109: -1.239183768916
110: -1.221730476396
111: -1.2042771838761
112: -1.1868238913561
113: -1.1693705988362
114: -1.1519173063163
115: -1.1344640137963
116: -1.1170107212764
117: -1.0995574287564
118: -1.0821041362365
119: -1.0646508437165
120: -1.0471975511966
121: -1.0297442586767
122: -1.0122909661567
123: -0.99483767363677
124: -0.97738438111682
125: -0.95993108859688
126: -0.94247779607694
127: -0.92502450355699
128: -0.90757121103705
129: -0.89011791851711
130: -0.87266462599716
131: -0.85521133347722
132: -0.83775804095728
133: -0.82030474843734
134: -0.80285145591739
135: -0.78539816339745
136: -0.76794487087751
137: -0.75049157835756
138: -0.73303828583762
139: -0.71558499331768
140: -0.69813170079773
141: -0.68067840827779
142: -0.66322511575785
143: -0.6457718232379
144: -0.62831853071796
145: -0.61086523819802
146: -0.59341194567807
147: -0.57595865315813
148: -0.55850536063819
149: -0.54105206811824
150: -0.5235987755983
151: -0.50614548307836
152: -0.48869219055841
153: -0.47123889803847
154: -0.45378560551853
155: -0.43633231299858
156: -0.41887902047864
157: -0.4014257279587
158: -0.38397243543875
159: -0.36651914291881
160: -0.34906585039887
161: -0.33161255787892
162: -0.31415926535898
163: -0.29670597283904
164: -0.27925268031909
165: -0.26179938779915
166: -0.24434609527921
167: -0.22689280275926
168: -0.20943951023932
169: -0.19198621771938
170: -0.17453292519943
171: -0.15707963267949
172: -0.13962634015955
173: -0.1221730476396
174: -0.10471975511966
175: -0.087266462599716
176: -0.069813170079773
177: -0.05235987755983
178: -0.034906585039887
179: -0.017453292519943
180: -1.2246467991474E-16
181: 0.017453292519943
182: 0.034906585039887
183: 0.05235987755983
184: 0.069813170079773
185: 0.087266462599716
186: 0.10471975511966
187: 0.1221730476396
188: 0.13962634015955
189: 0.15707963267949
190: 0.17453292519943
191: 0.19198621771938
192: 0.20943951023932
193: 0.22689280275926
194: 0.24434609527921
195: 0.26179938779915
196: 0.27925268031909
197: 0.29670597283904
198: 0.31415926535898
199: 0.33161255787892
200: 0.34906585039887
201: 0.36651914291881
202: 0.38397243543875
203: 0.4014257279587
204: 0.41887902047864
205: 0.43633231299858
206: 0.45378560551853
207: 0.47123889803847
208: 0.48869219055841
209: 0.50614548307836
210: 0.5235987755983
211: 0.54105206811824
212: 0.55850536063819
213: 0.57595865315813
214: 0.59341194567807
215: 0.61086523819801
216: 0.62831853071796
217: 0.6457718232379
218: 0.66322511575784
219: 0.68067840827779
220: 0.69813170079773
221: 0.71558499331768
222: 0.73303828583762
223: 0.75049157835756
224: 0.76794487087751
225: 0.78539816339745
226: 0.80285145591739
227: 0.82030474843733
228: 0.83775804095728
229: 0.85521133347722
230: 0.87266462599716
231: 0.89011791851711
232: 0.90757121103705
233: 0.92502450355699
234: 0.94247779607694
235: 0.95993108859688
236: 0.97738438111682
237: 0.99483767363677
238: 1.0122909661567
239: 1.0297442586767
240: 1.0471975511966
241: 1.0646508437165
242: 1.0821041362365
243: 1.0995574287564
244: 1.1170107212764
245: 1.1344640137963
246: 1.1519173063163
247: 1.1693705988362
248: 1.1868238913561
249: 1.2042771838761
250: 1.221730476396
251: 1.239183768916
252: 1.2566370614359
253: 1.2740903539559
254: 1.2915436464758
255: 1.3089969389957
256: 1.3264502315157
257: 1.3439035240356
258: 1.3613568165556
259: 1.3788101090755
260: 1.3962634015955
261: 1.4137166941154
262: 1.4311699866353
263: 1.4486232791553
264: 1.4660765716752
265: 1.4835298641952
266: 1.5009831567151
267: 1.5184364492351
268: 1.535889741755
269: 1.553343034275
270: 1.5707963267949
271: -1.553343034275
272: -1.535889741755
273: -1.5184364492351
274: -1.5009831567151
275: -1.4835298641952
276: -1.4660765716752
277: -1.4486232791553
278: -1.4311699866354
279: -1.4137166941154
280: -1.3962634015955
281: -1.3788101090755
282: -1.3613568165556
283: -1.3439035240356
284: -1.3264502315157
285: -1.3089969389957
286: -1.2915436464758
287: -1.2740903539559
288: -1.2566370614359
289: -1.239183768916
290: -1.221730476396
291: -1.2042771838761
292: -1.1868238913561
293: -1.1693705988362
294: -1.1519173063163
295: -1.1344640137963
296: -1.1170107212764
297: -1.0995574287564
298: -1.0821041362365
299: -1.0646508437165
300: -1.0471975511966
301: -1.0297442586767
302: -1.0122909661567
303: -0.99483767363677
304: -0.97738438111682
305: -0.95993108859688
306: -0.94247779607694
307: -0.925024503557
308: -0.90757121103705
309: -0.89011791851711
310: -0.87266462599716
311: -0.85521133347722
312: -0.83775804095728
313: -0.82030474843733
314: -0.80285145591739
315: -0.78539816339745
316: -0.76794487087751
317: -0.75049157835756
318: -0.73303828583762
319: -0.71558499331768
320: -0.69813170079773
321: -0.68067840827779
322: -0.66322511575785
323: -0.6457718232379
324: -0.62831853071796
325: -0.61086523819802
326: -0.59341194567807
327: -0.57595865315813
328: -0.55850536063819
329: -0.54105206811824
330: -0.5235987755983
331: -0.50614548307836
332: -0.48869219055841
333: -0.47123889803847
334: -0.45378560551853
335: -0.43633231299858
336: -0.41887902047864
337: -0.4014257279587
338: -0.38397243543875
339: -0.36651914291881
340: -0.34906585039887
341: -0.33161255787892
342: -0.31415926535898
343: -0.29670597283904
344: -0.27925268031909
345: -0.26179938779915
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348: -0.20943951023932
349: -0.19198621771938
350: -0.17453292519943
351: -0.15707963267949
352: -0.13962634015955
353: -0.1221730476396
354: -0.10471975511966
355: -0.087266462599717
356: -0.069813170079774
357: -0.05235987755983
358: -0.034906585039886
359: -0.017453292519943
360: -2.4492935982947E-16