If 3 cos 2a = n cos 8a, then what is the value of cot 5a cot 3a?
Answer
Correct Answer : b ) \(\frac{n+3} { n-3}\)
Explanation :3 cos 2a = n cos 8a
⇒\({n \over 3}={cos \ 2a \over cos \ 8a}\)
Using componendo dividendo
⇒\({n+3 \over n-3}={cos \ 2a+cos \ 8a \over cos \ 2a-cos \ 8a}\)
We know,
\(cosA+cosB=2cos({A+B \over 2})cos({A-B \over 2})\)
\(cosA-cosB=2sin({A+B \over 2})sin({B-A \over 2})\)
Thus,
⇒\({n+3 \over n-3}={2 \ cos \ 5a \ × \ cos \ 3a \over 2 \ sin \ 5a \ × \ sin \ 3a}\)
⇒\(cot \ 5a \ cot \ 3a={n+3 \over n-3}\)
Hence, (b) is the correct answer.
Such type of question is asked in various government exams like SSC CGL, SSC MTS, SSC CPO, SSC CHSL, RRB JE, RRB NTPC, RRB GROUP D, RRB OFFICER SCALE-I, IBPS PO, IBPS SO, RRB Office Assistant, IBPS Clerk, RBI Assistant, IBPS RRB OFFICER SCALE 2&3, UPSC CDS, UPSC NDA, UP SI etc.
Read Daily Current Affairs, Banking Awareness, Hindi Current Affairs, Word of the Day, and attempt free mock tests at PendulumEdu and boost your preparation for the actual exam.
Share QOTD
Popular Blog
Paris Olympics 2024: Brief History of Olympics, Winners at Paris Olympics, Related Facts
Read More
Highlights of Union Budget 2024-25
Read More
Highlights of Interim Budget 2024
Read More
150+ Paryayvachi Shabd in Hindi - पर्यायवाची शब्द
Read MoreLatest Current Affairs
Daily Current Affairs and GK | 13 December 2024
Read More
Daily Current Affairs and GK | 12 December 2024
Read More
Daily Current Affairs and GK | 11 December 2024
Read More
Daily Current Affairs and GK | 10 December 2024
Read More
Daily Current Affairs and GK | 8 and 9 December 2024
Read MoreLatest Banking Awareness
Banking Awareness of 8, 9 and 10 December 2024
Read More
Banking Awareness of 6 and 7 December 2024
Read More
Banking Awareness of 3, 4 and 5 December 2024
Read More
Banking Awareness of 1 and 2 December 2024
Read More
Banking Awareness of 27, 28 and 29 November 2024
Read More
Comments