Question

Show that cos42 + cos78 + cos162 = 0

Answer 1

Step-by-step explanation:

we HAVE THE TASK,

Show that cos42 + cos78 + cos162 = 0

SOLUTION:-

we have,

cos 42+cos78+cos 162

Then,

we know that ,

cos(60-18)+cos(60+18)+cos(180-18)

according to the formula

= cos 60 . cos 18 + sin 60 . sin 18 + cos 60 . cos 18 – sin60.sin 18 – cos 18

=2cos 60 . cos 18 – cos 18= 2. ½ . cos 18 – cos 18 =0

Answer 2

Answer:

Hi

Step-by-step explanation:

ur answer is

Cos42+cos78+cos162

=cos(60-18)+cos(60+18)+cos(180-18)

by applying formula

cos60. cos18+ sin60. sin18+ cos 60. cos 18-sin60. sin18- cos 18

2cos60. cos18-cos18

2.1/2.cos18-cos 18=0

Hope it helps u.....