Question

Find the value of cos10 + cos50

Answer 1

Hey there!

cosC + cosD = 2 cos(C+D/2) cos ( C-D/2)

cos10 + cos50= 2 cos(10+50/2) cos ( 10-50/2)

= 2 cos ( 60/2) cos(-40/2)

we know Cos ( -∅) = cos∅

so

= 2 cos 30 cos 20

= 2 *√3/2 cos20

=√3 cos20

=√3 sin70

hope helped !

Answer 2

Apply sum and difference formula i.e
cos C + cos D = 2cos (C+D/2).cos (C-D/2)

cos 10 + cos 50 = 2cos (10+50/2).cos (10-50/2)

= 2 cos 30 . cos 20
= 2 . √3/2. cos 20
= ✓3 cos 20

Hope This Helps You!