Solve this:

Q.1  In $∆\mathrm{ABC} , \mathrm{if} {\sin }^2\left(\frac{\mathrm{A}}{2}\right)- {\sin }^2\left(\frac{\mathrm{B}}{2}\right)+{\sin }^2\left(\frac{\mathrm{C}}{2}\right)+2 \cos \left(\frac{\mathrm{A}}{2}\right) \sin$ the value of k is 

      (A) 1 

      (B) 2

      (C) –1

      (D) –2

 

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