Trigonometry


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|ﬢ   θ \
+-------+

Definitions

Few values

| Radian | Degree | sin  | cos  | tan  |
|--------+--------+------+------+------|
| 0      |      0 | 0    | 1    | 0    |
| π/6    |     30 | 1/2  | √3/2 | 1/√3 |
| π/4    |     45 | 1/√2 | 1/√2 | 1    |
| π/3    |     60 | √3/2 | 1/2  | √3   |
| π/2    |     90 | 1    | 0    | ∞    |

Squared

From Wikipedia:

|        | sin         | cos         | tan         | cosec         | sec         | cot         |
|--------+-------------+-------------+-------------+---------------+-------------+-------------|
|        |             |             |             |               |             |             |
|        |             |             |    tan²θ    |      1        |  sec²θ - 1  |     1       |
| sin    | sin²θ       | 1 - cos²θ   | ─────────── | ───────────   | ─────────── | ─────────── |
|        |             |             | 1 + tan²θ   |    sin²θ      |    sec²θ    | 1 + cot²θ   |
|--------+-------------+-------------+-------------+---------------+-------------+-------------|
|        |             |             |             |               |             |             |
|        |             |             |    1        | cosec²θ - 1   |     1       |    cot²θ    |
| cos    | 1 - sin²θ   | cos²θ       | ─────────── | ───────────   | ─────────── | ─────────── |
|        |             |             | 1 + tan²θ   |   cosec²θ     |    sec²θ    | 1 + cot²θ   |
|        |             |             |             |               |             |             |
|--------+-------------+-------------+-------------+---------------+-------------+-------------|
|        |             |             |             |               |             |             |
|        |   sin²θ     | 1 - cos²θ   |             |      1        |             |    1        |
| tan    | ─────────── | ─────────── | tan²θ       | ───────────── | sec²θ - 1   | ─────────── |
|        | 1 - sin²θ   |    cos²θ    |             |  cosec²θ - 1  |             | cot²θ       |
|        |             |             |             |               |             |             |
|--------+-------------+-------------+-------------+---------------+-------------+-------------|
|        |             |             |             |               |             |             |
|        |    1        |     1       |             | 1 + tan²θ     | sec²θ       |             |
| cosec  | ───────     | ─────────── | tan²θ       | ───────────   | ─────────-  | 1 + cot²θ   |
|        |  sin²θ      |  1 - cos²θ  |             |    tan²θ      | sec²θ - 1   |             |
|        |             |             |             |               |             |             |
|--------+-------------+-------------+-------------+---------------+-------------+-------------|
|        |             |             |             |               |             |             |
|        |    1        |    1        |             |   cosec²θ     |             | 1 + cot²θ   |
| sec    | ──────────  | ────────    | 1 + tan²θ   | ───────────   | sec²θ       | ──────────  |
|        | 1 - sin²θ   |  cos²θ      |             | cosec²θ - 1   |             |    cot²θ    |
|        |             |             |             |               |             |             |
|--------+-------------+-------------+-------------+---------------+-------------+-------------|
|        |             |             |             |               |             |             |
|        | 1 - sin²θ   |  cos²θ      |   1         |               |    1        |             |
| cot    | ──────────  | ──────────  | ──────      | cosec²θ - 1   | ───────     | cot²θ       |
|        | sin²θ       | 1 - cos²θ   |  tanθ       |               |  sec²θ      |             |
|        |             |             |             |               |             |             |

Reflections

| Function | -θ      | π/2 - θ | π - θ  | 3π/4 - θ |
|----------+---------+---------+--------+----------|
| sinθ     | -sinθ   | cosθ    | sinθ   | -cosθ    |
|----------+---------+---------+--------+----------|
| cosθ     | cosθ    | sinθ    | -cosθ  | -sinθ    |
|----------+---------+---------+--------+----------|
| tanθ     | -tanθ   | cotθ    | -tanθ  | cotθ     |
|----------+---------+---------+--------+----------|
| cosecθ   | -cosecθ | secθ    | cosecθ | -secθ    |
|----------+---------+---------+--------+----------|
| secθ     | secθ    | cosecθ  | -secθ  | -cosecθ  |
|----------+---------+---------+--------+----------|
| cotθ     | -cotθ   | tanθ    | -cotθ  | tanθ     |

Periodicity

Functions with period :

| Function | θ ± (π/2) | +π      |
|----------+-----------+---------|
| sin      | ± cosθ    | -sinθ   |
| cos      | ∓ sinθ    | -cosθ   |
| cosec    | ± secθ    | -cosecθ |
| sec      | ∓ cosecθ  | -secθ   |

Functions with period π:

| Function | θ ± (π/4) | +(π/2) |
|----------+-----------+--------|
|          | tanθ ± 1  |        |
| tan      | ───────── | ─cotθ  |
|          | 1 ∓ tanθ  |        |
|----------+-----------+--------|
|          | cotθ ∓ 1  |        |
| cot      | ───────── | ─tanθ  |
|          | 1 ± cotθ  |        |

Angle sum

| sin(A±B)        | sinA.cosB ± cosA.sinB       |
|-----------------+-----------------------------|
| cos(A±B)        | cosA.cosB ∓ sinA.sinB       |
|-----------------+-----------------------------|
|                 | tanA ± tanB                 |
| tan(A±B)        | ────────────────            |
|                 | 1 ∓ tanA.tanB               |
|-----------------+-----------------------------|
|                 | secA.secB.cosecA.cosecB     |
| cosec(A±B)      | ──────────────────────────  |
|                 | secA.cosecB ± cosecA.secB   |
|-----------------+-----------------------------|
|                 | secA.secB.cosecA.cosecB     |
| sec(A±B)        | ──────────────────────────  |
|                 | cosecA.cosecB ∓ secA.secB   |
|-----------------+-----------------------------|
|                 | cotA.cotB ∓ 1               |
| cot(A±B)        | ─────────────               |
|                 | cotB ∓ cotA                 |
|-----------------+-----------------------------|
|                 |      ⎛                    ⎞ |
| sin⁻¹x ± sin⁻¹y | sin⁻¹⎜x√(1-y²) ± y√(1-x²) ⎟ |
|                 |      ⎝                    ⎠ |
|-----------------+-----------------------------|
|                 |      ⎛                    ⎞ |
| cos⁻¹x ± cos⁻¹y | cos⁻¹⎜xy ∓ √[(1-x²)(1-y²)]⎟ |
|                 |      ⎝                    ⎠ |
|-----------------+-----------------------------|
|                 |      ⎛  x ± y  ⎞            |
| tan⁻¹x ± tan⁻¹y | tan⁻¹⎜─────────⎟            |
|                 |      ⎝  1 ∓ xy ⎠            |
|-----------------+-----------------------------|
|                 |      ⎛  xy ∓ 1 ⎞            |
| cot⁻¹x ± cot⁻¹y | cot⁻¹⎜─────────⎟            |
|                 |      ⎝  y ± x  ⎠            |

Double angle

|         |               |                    |   2.tanθ     |              |
| sin2θ   | 2.sinθ.cosθ   | (sinθ + cosθ)² ─ 1 | ──────────── |              |
|         |               |                    | 1 + tan²θ    |              |
|---------+---------------+--------------------+--------------+--------------|
|         |               |                    |              | 1 - tan²θ    |
| cos2θ   | cos²θ - sin²θ | 2.cos²θ - 1        | 1 - 2.sin²θ  | ──────────── |
|         |               |                    |              | 1 + tan²θ    |
|---------+---------------+--------------------+--------------+--------------|
|         |    2.tanθ     |                    |              |              |
| tan2θ   | ───────────── |                    |              |              |
|         |  1 - tan²θ    |                    |              |              |
|---------+---------------+--------------------+--------------+--------------|
|         | secθ.cosecθ   | 1 + tan²θ          |              |              |
| cosec2θ | ───────────── | ─────────          |              |              |
|         |      2        |   2.tanθ           |              |              |
|---------+---------------+--------------------+--------------+--------------|
|         |     sec²θ     | 1 + tan²θ          |              |              |
| sec2θ   | ───────────── | ─────────          |              |              |
|         | 2 - sec²θ     | 1 - tan²θ          |              |              |
|---------+---------------+--------------------+--------------+--------------|
|         |   cot²θ - 1   |  1 - tan²θ         |              |              |
| cot2θ   | ───────────── | ───────────        |              |              |
|         |    2.cotθ     |   2.tanθ           |              |              |

Triple angle

|         |                 |           ⎛ π     ⎞    ⎛ π     ⎞ |
| sin3θ   | 3.sinθ - 4sin³θ | 4.sinθ.sin⎜─── - θ⎟.sin⎜─── + θ⎟ |
|         |                 |           ⎝ 3     ⎠    ⎝ 3     ⎠ |
|---------+-----------------+----------------------------------|
|         |                 |           ⎛ π     ⎞    ⎛ π     ⎞ |
| cos3θ   | 4cos³θ - 3.cosθ | 4.cosθ.cos⎜─── - θ⎟.cos⎜─── + θ⎟ |
|         |                 |           ⎝ 3     ⎠    ⎝ 3     ⎠ |
|---------+-----------------+----------------------------------|
|         | 3.tanθ - tan³θ  |         ⎛ π     ⎞    ⎛ π     ⎞   |
| tan3θ   | ─────────────── | tanθ.tan⎜─── - θ⎟.tan⎜─── + θ⎟   |
|         |  1 - 3.tan²θ    |         ⎝ 3     ⎠    ⎝ 3     ⎠   |
|---------+-----------------+----------------------------------|
|         |     cosec³θ     |                                  |
| cosec3θ | ─────────────   |                                  |
|         | 3.cosec²θ - 4   |                                  |
|---------+-----------------+----------------------------------|
|         |     sec³θ       |                                  |
| sec3θ   | ─────────────   |                                  |
|         | 4 - 3.sec²θ     |                                  |
|---------+-----------------+----------------------------------|
|         | 3.cotθ - cot³θ  |                                  |
| cot3θ   | ──────────────  |                                  |
|         |  1 - 3.cot²θ    |                                  |

Small angle approximation

From Wikipedia:

sinθ ≈ θ