1-2sin²12分之25π=

1-2sin²12分之25π=
1-2sin²12分之25π=

1-2sin²12分之25π=
1--2[sin(25派/12)]^2
=cos[2*(25派/12)]
=cos(25派/6)
=cos(4派+派/6)
=cos(派/6)
=(根号3)/2.