(2х+х)*2=54. 9*2=18
3х=27. S=18*9=162
х=9.
2 3/5×3/5=13/5×3/5=38/25=1 13/25
Cos A = 2/3
sin² A =1 - cos² A = 1 - 4/9 = 5/9
sin A = √5 /3
sinA 5 * 3
tg A = ------- = ------------ = √5 /3
cosA √5 * 9
ctg= 1/ tgA = 3/√5
А) (18 + x) + 12 = 18 + x + 12 = x + 30
б) 25 - (а - b + 28) = 25 - а + b - 28 = -а + b -3;
в) (25 - z) + (t - 18) = 25 - z + t -18 = t - z + 7;
г) -(р + 3) + (q - 7) = -p - 3 + q - 7 = -p + q - 10.