Question

ДОВЕДІТЬ ТОТОЖНІСТЬ
ЗАВДАННЯ НА ФОТО

Answer 1

1−4sin10sin70
​


[2sinAsinB=cos(A−B)−cos(A+B)]

=
2sin10
1−2[cos(10−70)−cos(10+70)]
​


[cos(−θ)=cosθ]

=
2sin10
1−2cos60+2cos80
​


=
2sin10
1−2(1/2)+2cos80
​
=
sin10
cos80
​


[cos(90−θ)=sinθ,∴cos(90−10)=sin10]

=
sin10
sin10
​
=1.