Question

Помогите с решением!?
ДОКАЖИТЕ РАВЕНСТВО:

 

1)sin105*cos105=-14

 

2)cos75+sin75=1

Answer 1

1)sin105*cos105 = sin(90+15)*cos(90+15) = sin15*(-cos15) = -1/2sin30 =  = -14.
2)cos75 + sin75 = √2cos(45-75) = √2cos(-30) = √2cos(+30) = √2√3/2 = =√(3/2) - не 1 ???
Можно по другому варианту:
cos75+sin75 = cos(90-15) + sin75 = sin15 +sin75 = 2sin((15+75)/2)*cos((15-75)/2) = 2sin45*cos(-30) = 2(√2/2)(√3/2) = = √(3/2) - не 1 ???