2 a) [sin(π+t)]² -[sin(π-t)]² = (-sint)² +(sint)² =2sin²t
b) [cos(π/2+t)]/[sin(π-t) · tg(-t) = (-sint)/[sint·(-tgt)] = 1/tgt = ctgt
3. sin(π/2+t) - cos(π+t) +1 = 0
cost -(-cost) +1 = 0
cost = -1/2
t= π +/-π/3 +2πk = (2k+1)·π +/-π/3 k∈Z
6. f(sinx) = 3sin²x +2sinx -1 = 3(1-cos²x) + 2sinx -1 =
= 3 -3cos²x +2sinx -1 = 2sinx - 3cos²x +2