132-9(х-5)=69
123-9х+45=69
177-9х=69
9х=69-177
-9х=-108
х=-108:(-9)
х=12
4sin^2 x - 2 sin x * cos x - sin^2 x - cos ^2 x = 0 ( : cos^2 x)
4 tg^2x - 2 tg x - tg x - 1 = 0
tg x = l, x ≠ p/2 + pn, n ∈ Z
4l^2 - 3 l - 1 = 0
D= 9+ 16= 25;
x(1,2) = 3+5/8 = 1; 3-5/8 = -1/2;
tg x = 1;
x = p/4 + pm, m ∈ Z.
tg x = 1/2
x = arctg 1/2 + pk, k ∈ Z.
ОТВ:21.......................
125*(482+118)=125*600=75000
(996+276)*905=1272*905=1151160
(3700+2500):200=6200:200=31
3200:(280-200)=3200:80=40