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If a= 3, b =4 , c = 5 then cos ""( A)...

If a= 3, b =4 , c = 5 then ` cos ""( A)/(2) =`

A

` (2)/(sqrt( 10))`

B

` ( 1)/( sqrt( 10 ))`

C

` ( 3)/(sqrt(10)) `

D

` ( 4)/(sqrt( 10 ))`

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The correct Answer is:
C
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AAKASH SERIES-PROPERTIES OF TRIANGLES-PRACTICE EXERCISE
  1. (a+b+c)/( a+b+c) =

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  2. If a= 5 , b-=12 , c=13 then tan ""(A)/(2) =

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  3. If a= 3, b =4 , c = 5 then cos ""( A)/(2) =

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  4. In Delta ABC , if a = 5 , b= 6 and c= 7 " then " cos ^(2) C //2 =

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  5. In Delta ABC , if angle A = 60 ^(@) then ( 1+ (a)/(c ) +(b) /...

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  6. Show that cot ""(A)/(2) + cot "" ( B)/(2) + cot "" ( C ) /(2)...

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  7. ((a^(2))/( sin A)+( b^(2))/(sin B) + ( c^(2))/( sin C) ) ( sin ""(A)/...

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  8. In Delta ABC ,(a+b+c) (tan ""(A)/(2) +tan ""(B)/(2) ) tan "" ( C) /...

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  9. In Delta ABC , if c= (a+b) sin theta and cos theta = ( k sqrt (ab))...

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  10. In Delta ABC , c cos ^(2) "" ( A)/(2) +a cos ^(2) "" ( C ) /(2) i...

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  11. In Delta ABC , a sin ^(2) "" ( C ) /(2) + c sin ^(2) "" (A ) /(2) ...

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  12. In Delta ABC , tan "" (A)/(2) , tan "" (B)/(2) are in H.P. A,b,c ...

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  13. In Delta ABC , if (a)/( c ) = (sin (A-B))/( sin (B-C)) , " then " ...

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  14. In Delta ABC , if cot "" (A)/(2) , cot "" ( B)/(2) , cot "" (C )/(2...

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  15. In Delta , if cot "" (A)/(2) : cot : (B )/(2) : cot ""( C )/(2) =...

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  16. In Delta ABC , if ( sin A)/(4) = (sin B)/(5) = (sin C)/( 6) then th...

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  17. In Delta ABC , if a: b: c = 3: 4:5 then sin A : sin B : sin C =

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  18. Cot A +Cot B +cot C =

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  19. If 4,5 are two sides of a triangle and included angle 60 ^(@) , ...

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  20. Area of triangle is 75 cm^(2) and two of its sides 20 cm, 15cm ,t...

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