3cos^2 pi x +4cos pi x-7=o

Cosπx = t 3t² +4t - 7 = 0 D= b² - 4ac = 16 -4*3*(-7) = 100 t1 = (-4+10)/6 = 1 t2 = (-4 -10)/6 = -14/6 = -7/3 a) t = 1 Cosπx = 1 πx = 2πk , k ∈Z x = 2k, k ∈Z б) Cosπx = -7/3 (нет решений) Ответ: х= 2k , k∈Z