найти 1 член геометрической прогрессии y5=3/4 q=-1/4

b5 = 3/4q = - 1/4b1*q^4 = 3/4b1 = 3/4 : q^4b1 = 3/4 * 1/q^4b1 = 3/4* 1/(-1/4)^4 b1 = 3/4*256b1 = 192