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
Highlights of Interim Budget 2024
Read More
150+ Paryayvachi Shabd in Hindi - पर्यायवाची शब्द
Read More
Highlights of G20 Summit 2023
Read More
SSC CHSL Tier 1 Exam Analysis 2023 - Questions Asked from 2 to 22 August 2023
Read MoreLatest Current Affairs
Daily Current Affairs and GK | 26 and 27 April 2024
Read More
Daily Current Affairs and GK | 25 April 2024
Read More
Daily Current Affairs and GK | 24 April 2024
Read More
Daily Current Affairs and GK | 23 April 2024
Read More
Daily Current Affairs and GK | 21 and 22 April 2024
Read More
Comments