1) (4-х)(4+х)
2) (n_25)(n+25)
3) (y-0.5)(y+0.5)
4) (5/6-y)(5/6+y)
5) (0.5-5/6)(0.5+5/6)
sin2a+sin6a=2sin4a cos2a
cos2a+cos6a=2coa4a cos2a
(sin2a+sin6a)/(cos2a+cos6a)=(2sin4a cos2a)/(2coa4a cos2a)=sin4a/cos4a=tg4a