Flag Trigonometry> what is thw solution for prove that :cos6...
question mark

what is thw solution for
prove that :cos6A+6cos4A+15cos2A+10

siddharth parihar , 8 Years ago
Grade 11
anser 1 Answers
Lata

Last Activity: 8 Years ago

0
simply write 6A = 3(2A) and then evaluate it with the aid of cos2A formula. Similarly, write 4A as 2(2A) and evaluate by the same formula. 
finally, you get a cubic in cos2A. take 2A as some x, and make the entire expression, equal to zero.(just for finding A). 
-1 satisfies the equation which looks like this : cos^3(x)(-> cosine cubed x) + 3cos^2(x) + 3cos(x) + 1 = 0. 
cosx = -1. The principal value is just x = pi. Therefore, 2A = pi. A = 90 degrees. 
Substitute this A in the question, and yeah, you get 0. :)

Provide a better Answer & Earn Cool Goodies

Enter text here...
star
LIVE ONLINE CLASSES

Prepraring for the competition made easy just by live online class.

tv

Full Live Access

material

Study Material

removal

Live Doubts Solving

assignment

Daily Class Assignments


Ask a Doubt

Get your questions answered by the expert for free

Enter text here...