Question

Please explain the marked part of the sum (trigonometry ---> sums and products) given in the attachment. Please answer this fast. Tomorrow is exam. Please don't spam it.

Answer 1

Answer:

Step-by-step explanation:

Answer 2

HIIII.......{∆}

THERE IS YOUR EXPLANATION....{¶}

THERE ARE SEVERAL PROPERTIES USED IN THIS SOLN. I WILL DISCUSS ONE BY ONE...

FOR......

$2 \cos( 20) \cos(80) \\ \\ as \: we \: know ..... \\ \\ 2 \cos( \alpha ) \cos( \beta ) = \cos( \alpha + \beta ) + \cos( \alpha - \beta ) \\ \\ 2 \cos(20) \cos(80) = \cos(80 + 20) + \cos(80 - 20) \\ \\ \cos(100) + \cos(60)$

THIS THE FIRST PART OF THE SOLN.....{∆}

PART II

$second \: part \: is \: wrongly \: solved \\ \\ firstly \: we \: put \: \: the \: value \ \\ : of \: \cos(60) \: and \: than \: solved \\ \: the \: remaining \: question \: and \: \\ than \: right \: \cos(100) = \cos(90 + 10) \\ \\ - \sin(10)$

HOPE YOU LIKE IT.....

BYE VAMP.....