Q4 of 164 Page 44

Show that

cos 20° cos 70° – sin 70° sin 20° = 0


Simplifying the left hand side:

⇒ cos 20° cos 70° – cos(90–70)° cos (90–20)°


⇒ cos 20° cos 70° – cos 20° cos 70°


⇒ 0


Which is equal to right hand side.


Hence proved.


More from this chapter

All 164 →
4

Show that

cos 48° – sin 42° = 0

 4

Show that

cos 20° cos 70° – sin 70° sin 20° = 0

 4

Show that

sin (90° – θ)tan θ = sin θ

 4

Show that

sin (90° – θ)tan θ = sin θ