Question

Cos 20+cos 100+cos 140=cos90

Answer 1

Answer:

cos350 is the answer I don't know but tellintelling you

Answer 2

Step-by-step explanation:

(cos 140+cos20) +sin(90+10)

using identies

* 2cosC+D/2 cos C-D/2

* 2cos 140+20/2 cos 140-20/2 + cos10 (sin90+Q=cosQ)

* 2Cos80 cos60+cos10

*2x1/2 cos80 +cos10 (cos60=1/2)

* cos80+cos10

* cos90

hence proved