1). d=9-12=-3
a14= 12-3(14-1)= 12-3*13= 12-39=-27
2). b11= 2 ; b9 = 34 ; d-?
b11=b1+10d
b9=b1+8d
b1+10d=2
b1+8d=34
-2d=32
d=32/(-2)
d=-16 разность прогрессии
3). S51= 2*12+2(51-1)*51/2 = (24+100)*51/2 =124*51/2=6324/2=3162
4). bn= -2-3n. S10-?
b1=-2-3*1=-5 ; b2=-2-3*2= -8
s10=2*(-5)-3(10-1)*10/2=(-10-27)*5=-37*5=-185
Б)5^22*(5^2)^3 5^22*5^6 5^27
_____________ = _____ ___________ = _________ = 1
5^27 5^27 5^27
7×(2.5-x)(5/3+3)=0
7×(2.5-x)×14/3=0
245/3-98/3x=0
245-98x=0
X=2.5