5х<-11+1
5x<-10
x<-10/5
x<-2
x∈(-∞; -2)
A1=5 a8=a1+7d
a2=1 d=a2-a1=1-5=-4
a3=-3 a8=5+7×(-4)=5-28=-23
a4=-7 (a8-это восьмой член)
А) 2х + 3х = (2+3)*х = 5х
б) 3m + 5m = (3+5)*m = 8m
г) а + 4а + а = (1+4+1)*а = 6а
д) 2а + 4а + 6а = (2+4+6)*а = 12а
е) 4ab + ab + 12ab = (4+1+12)*ab = 17ab
ж) 17а² + 13а³ + 11а³ = 17а² + (13+11)*а³ = 17а² + 24а³
з) 15а²b + 14а²b + 7а²b = (15+14+7)*a²b = 36a²b
и) 43сe² + (-17ce²) + 11ce² = (43 - 17 +11)*ce² = 37ce²
к) 25b²c² + (-27b²c²) + 7b²c² = (25 - 27 + 7)*b²c² = 5b²c²
Cos(a+b)= cosa.cosb-sina.sinb,
cos2a = cos kv a- sin kv a
sin2b = 2.sinb . cosb.
Nado znat sinb a cos a.
sin kv b = 1- cos kv b = 1-9/25=16/25, sinb = 4/5
cos kv a = 1-sin kv a = 1-64/289 = 225/289, cos a = 15/17
cos(a+b)=15/17.3/5 - 8/17.4/5 =
cos 2a = 225/289 - 64/289 = 161/289
sin2b = 2. 4/5.3/5 = 24/25