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Prove that :sin 420^@ cos390^@+cos(-300^...

Prove that :`sin 420^@ cos390^@+cos(-300^@)sin(-330^@)=1`

A

0

B

1

C

2

D

`-1`

Text Solution

Verified by Experts

The correct Answer is:
B
Given expression
`=sin(360^(@)+60^(@)).cos(360^(@)+30^(@))+cos(360^(@)-60^(@))`
`(-sin(360^(@)-30^(@))`
`=sin60^(@).cos30^(@)+cos60^(@)sin30^(@)=sin(60^(@)+30^(@))`
`=sin90^(@)=1`
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