Answer :

strawberry99
cos​2​​A+cos​2​​C+2cosacosbcosc=1−cos​2​​B


os​2​​A+2cosacosbcosc=1−cos​2​​B−cos​2​​C


cos​2​​A=1−cos​2​​B−cos​2​​C−2cosacosbcoscosA=±√​1−cos​2​​B−cos​2​​C−2cosacosbcosc​

​​A=arccos(√​1−cos​2​​B−cos​2​​C−2cos(a)cos(b)cos(c)​​​),arccos(−√​1−cos​2​​B−cos​2​​C−2cos(a)cos(b)cos(c)​

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