RD Sharma - Mathematics

Book: RD Sharma - Mathematics

Chapter: 7. Values of Trigonometric Functions at Sum of Difference of Angles

Subject: - Class 11th

Q. No. 9 of Exercise 7.1

Listen NCERT Audio Books to boost your productivity and retention power by 2X.

9

Prove that: cos 7π/12 + cos π/12 = sin 5π/12 – sin π/12

7π/12 = 105°, π/12 = 15°; 5π/12 = 75°


LHS = cos 105° + cos 15°


= cos(90° + 15°) + sin(90° - 75°)


= -sin 15° + sin 75°


= sin 75° - sin 15° = RHS


Hence proved.


Chapter Exercises

More Exercise Questions

6

If SinA = 1/2, cosB = , where π/2<A < π And 0 <B < π/2, find the following:

(i) tan(A +B)(ii) tan(A -B)