×

#### Thank you for registering.

One of our academic counsellors will contact you within 1 working day.

Click to Chat

1800-1023-196

+91-120-4616500

CART 0

• 0

MY CART (5)

Use Coupon: CART20 and get 20% off on all online Study Material

ITEM
DETAILS
MRP
DISCOUNT
FINAL PRICE
Total Price: Rs.

There are no items in this cart.
Continue Shopping
```
Cos 20.cos100 plus cos100.cos140 minus cos140.cos200 is equal to
Cos 20.cos100  plus cos100.cos140 minus cos140.cos200   is   equal   to

```
8 months ago

Arun
25768 Points
```							cosA + cosB = 2[cos(A + B)/2][cos(A - B)/2] i.e. (1/2)(cosA + cosB) = [cos(A + B)/2][cos(A - B)/2] => cos20cos100 = (1/2)(cos120 + cos80) => cos100cos140 = (1/2)(cos240 + cos40) => -cos140cos200 = -(1/2)(cos340 + cos60) => (1/2)[cos120 + cos80 + cos240 + cos40 – cos340 – cos60] => (1/2)[-1/2 + cos80 – 1/2 + cos40 – cos340 – 1/2] => (1/2)[-3/2 + cos80 + cos40 – cos340] => (1/2)[-3/2 + 2cos60cos20 – cos340] => (1/2)[-3/2 + cos20 – cos340] => (1/2)[-3/2 + cos20 – cos(-20)] So, (1/2)(-3/2) = -3/4
```
8 months ago
Saurabh Koranglekar
10341 Points
```
```
8 months ago
Think You Can Provide A Better Answer ?

## Other Related Questions on Trigonometry

View all Questions »

### Course Features

• 731 Video Lectures
• Revision Notes
• Previous Year Papers
• Mind Map
• Study Planner
• NCERT Solutions
• Discussion Forum
• Test paper with Video Solution

### Course Features

• 31 Video Lectures
• Revision Notes
• Test paper with Video Solution
• Mind Map
• Study Planner
• NCERT Solutions
• Discussion Forum
• Previous Year Exam Questions