Ex 3.3, 11 - Prove that cos (3pi/4 + x) - cos (3pi/4 - x) - cos x + cos y formula

 

  1. Chapter 3 Class 11 Trigonometric Functions
  2. Serial order wise

Transcript

Ex 3.3, 11 Prove that cos (3 /4+x) cos (3 /4 x) = 2 sin x Taking L.H.S. cos (3 /4+x) cos (3 /4 x) = 2 sin (((3 /4 + x) + (3 /4 x))/2) sin (((3 /4 + x) (3 /4 x))/2) = 2 sin (((3 /4 + 3 /4) + ( ))/2) sin ((3 /4 + x 3 /4 + x)/2) = 2 sin (((3 /2 ))/2) sin (2x/2) = 2 sin (3 /4) sin ( ) Putting = 180 = 2 sin ((3 180 )/4) sin ( ) = 2 sin ("135 " ) sin ( ) = 2 sin ( 180" " 45" ") sin x = 2 sin 45 sin x = 2 1/ 2 sin x = - 2 2 1/ 2 sin x = - 2 sin x = R.H.S. Hence proved

About the Author

Davneet Singh's photo - Teacher, Computer Engineer, Marketer
Davneet Singh
Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 8 years. He provides courses for Maths and Science at Teachoo. You can check his NCERT Solutions from Class 6 to 12.