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If in a Delta ABC, a, b, c are in A.P ....

If in a `Delta ABC, a, b, c ` are in A.P . Then
` cos ((A- C)/( 2)) ` is equal to

A

` ( 1)/ (2) sin ""( B)/(2) `

B

`2 sin "" (B)/2`

C

` (1)/(3) sin ""( B)/(2) - 4 `

D

` 3 sin ""( B)/(2) `

Text Solution

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The correct Answer is:
B
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AAKASH SERIES-PROPERTIES OF TRIANGLES-EXERCISE - 1
  1. If tan ((A -B)/( 2)) = (1)/(3) tan ((A+B)/( 2)) then a : b is

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  2. If (b-c) cos A/2 = a ( sin k ) then k =

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  3. If in a Delta ABC, a, b, c are in A.P . Then cos ((A- C)/( 2)) ...

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  4. In Delta ABC,if 3a=b+c, then cot""B/2.cot""C/2=

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  5. If (a+b+c) (b+c-a) = 3bc then find angle A .

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  6. In Delta ABC, (b-c)^2 +4bc sin^2 (A//2)=

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  7. If 2 sin ""( A) /( 2) sin ""( C)/(2) = sin "" ( B) /(2) then a,b,c ...

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  8. If 2 cot ""( B)/(2) = cot "" (A) /( 2) + cot "" ( C )/(2) then a,b,...

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  9. In Delta ABC, if 3 tan ""A/2 tan""C/2=1 then a,b,c are in

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  10. Show that Delta =(a^(2))/( 2( cot B+ cot C ) )

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  11. a^(2) sin 2B+ b^(2) sin 2A =

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  12. If c^(2) = a^(2) + b^(2) then 4s ( s-a) ( s-b) ( s-c) =

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  13. ((a^(2) - b^(2) sin A sin B) /( 2 sin ( A- B)))

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  14. a cot A + b cos B + c cos C =

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  15. ( x) /( y ) + (y)/(z) , ( z)/(x) + (z)/(x) + (x)/(y) then the area of...

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  16. In Delta ABC, if a= 2, B=120^@, C=30^@, then the area of the triangle ...

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  17. The diameter of the circumcircle of the triangle whose sides 61,60,11 ...

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  18. If the length of side of an equilateral triangle is 10cm , then R =

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  19. If a cos B = b cos A then the triangle is

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  20. If a = 40 , c= 40 sqrt3, B = 30 ^(@) then nature of triangle is

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