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In a A B C ,\ ifb=20 ,\ c=21\ a n dsinA...

In a ` A B C ,\ ifb=20 ,\ c=21\ a n dsinA=3/5` find `adot`

A

12

B

13

C

14

D

15

Text Solution

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The correct Answer is:
B
`cos ^(2)A=1-sin^(2)A=1-((3)/(5))^(2)`
`=16/25`
`impliescos A=4/5`
`implies((20)^(2)+(21)^(2)-a^(2))/(2*20*21)=4/5`
`impliesa^(2)=169impliesa=13`
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