Maths-
General
Easy

Question

If sin B = 1/2 then 3cos B – 4 cos3 B =

  1. 0    
  2. 1/2    
  3. fraction numerator 1 over denominator 4 end fraction    
  4. fraction numerator 3 over denominator 4 end fraction    

The correct answer is: 0


    To find the value of the given expression
    S i n B equals space 1 divided by 2 space ​ space space space
because sin 30 space space ring operator space space equals space 1 divided by 2 space ​ space space space
therefore B equals 30 space space space
t h e space p u t space t h e space v a l u e space o f space B space i n space space space 3 cos B minus 4 cos cubed B
space rightwards double arrow 3 cos 3 space space minus 4 cos cubed space 30 space space
space because cos 30 equals space space 3 divided by 2 space ​ space space space ​ space space space
t h e n space rightwards double arrow 3 cross times 3 divided by 2 space ​ space space space ​ space space minus 4 cross times left parenthesis space 3 divided by 2 space right parenthesis cubed space space space equals 0

    Hence option 4 is correct

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