Question

प्रश्न.8. cos(-1080°) का मान ज्ञात कीजिये ?
2TOCIT​

Answer 1

In trigonometry, cos is referred to cosine of any angle. There are some formulae which must be followed while solving this type of problems.

Formulae:

1. cos(90° - A) = sinA
2. cos(90° + A) = - sinA
3. cos(180° - A) = - cosA
4. cos(180° + A) = - cosA
5. cos(270° - A) = - sinA
6. cos(270° + A) = sinA
7. cos(360° + A) = cosA
8. cos(360° - A) = cosA
9. cos(- A) = cosA

Step-by-step explanation:

Now, cos(- 1080°)

= cos1080°

= cos (3 * 360°)

= cos360°

= cos(360° + 0°)

= cos0°

= 1, since cos0° = 1

Answer:

The value of cos(- 1080°) is 1.

Answer 2

समाधान

निर्धारित करना है

cos(-1080°) का मान

समाधान

Step : 1

Write down the given expression cos(-1080°)

Step : 2

Cos is an even function

∴ cos(-1080°) = cos 1080°

Step : 3

Express 1080° in terms of 90°

1080° = ( 12 × 90° ) + 0°

Step : 4

The angle 1080° lies in Fourth Quadrant

Step : 5

$\sf{ \cos( - {1080}^{ \circ}) }$

$= \sf{ \cos {1080}^{ \circ} }$

$= \sf{ \cos( 12 \times {90}^{ \circ} + {0}^{ \circ}) }$

$= \sf{ \cos {0}^{ \circ} }$

$= 1$

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