Thank you for registering.

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

Please check your email for login details.
Close
MY CART (5)

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

ITEM
DETAILS
MRP
DISCOUNT
FINAL PRICE
Total Price: Rs.

⇐ BackProceed to Checkout ⇒
There are no items in this cart.
Continue Shopping

Question 8. . . . . . . . . . . . . . ?? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Question 8. . . . . . . . . . . . . . ?? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Question Image
Grade:11

2 Answers

Ajay
209 Points
5 years ago
Given\quad A+B+C\quad =\quad 180-----(1)\\ { sin }^{ 2 }A+{ sin }^{ 2 }B+{ sin }^{ 2 }C\\ =1/2(1-cos2A+1-cos2B+1-cos2C)\\ =1/2\left\{ 3-\left( cos2A+cos2B+cos2C \right) \right\} \\ =1/2\left\{ 3-\left( 2cos(A+B)cos(A-B)+cos2C \right) \right\} \\ From(1)\quad cos2C\quad =\quad cos(360-2A-2B)\quad \\ =\quad cos2(A+B)\quad =\quad 2{ cos }^{ 2 }(A+B)-1\\ Substituting\quad cos2C\quad we\quad have\\ =\quad 1/2\left\{ 3-\left( 2cos(A+B)cos(A-B)+2{ cos }^{ 2 }(A+B)-1 \right) \right\} \\ =1/2\left\{ 4-2cos(A+B)\left( cos(A-B)+{ cos }(A+B) \right) \right\} \\ from\quad (1)\quad cos(A+B)\quad =\quad cosC\quad \\ \\ =1/2(4-4cosCcosAcosB)\\ =2(1-cosCcosAcosB)\\
Ajay
209 Points
5 years ago
Slight correction last few steps....................................................................................................
from\quad (1)\quad cos(A+B)\quad =\quad -cosC\quad \\ \\ =1/2(4+4cosCcosAcosB)\\ =2(1+cosCcosAcosB)

Think You Can Provide A Better Answer ?

Provide a better Answer & Earn Cool Goodies See our forum point policy

Other Related Questions on Trigonometry

View all Questions »

ASK QUESTION

Get your questions answered by the expert for free

Register ICAT

Answer and earn gift vouchers

Win Gift vouchers upto Rs 500/-

View courses by askIITians

Design classes One-on-One in your own way with Top IITians/Medical Professionals

Click Here Know More

Complete Self Study Package designed by Industry Leading Experts

Click Here Know More

Live 1-1 coding classes to unleash the Creator in your Child

Click Here Know More

a Complete All-in-One Study package Fully Loaded inside a Tablet!

Click Here Know More