3а-(а-1)+(2а-5) = 3a - a +1 +2a-5 = 4a - 4 = 4(a-1)
12-8у-42= 6+4y
12y=-36
У=-36:12
У=-3
A) (tg a - ctg a)^2 = 16 = (tg a)^2 + 2*tg a * ctg a + (ctg a)^2 = [ tg a * ctg a = 1] =
= (tg a)^2 + (ctg a)^2 +2 = 16
(tg a)^2 + (ctg a)^2 = 14
б) (cos a + sin a)^2 = 1/9 = (cos a)^2 + 2 sin a * cos a + (sin a)^2 = 1 + sin 2a
sin 2a = -8/9
1 + 2/(tg a + ctg a) = 1+ 2/( sin a / cos a + cos a / sin a) = 1 + 2/ ( (sin^2 a + cos^2 a) / sin a*cos a) = 1+ 2 sin a*cos a/1 = 1+ sin 2a = 1 - 8/9 = 1/9
X\3 = arctg 3\2 + πn | * 3 , n∈Z
x= 3arctg 3\2 + 3πn , n∈Z