<span>Sn=b1*(1-q^n)/1-q
S3=b1*(1-q^3)/1-q
-105=b1*(1-4^3)/1-4
-105=b1-64b1/-3
b1-64b1=-105*(-3)
-63b1=315
b1=315/63
b1=-5
S5 = -5*(1-4^5)/1-4 = -5*(1-1024)/-3 = -5*(-1023)/-3 = 5115/-3 = -1705
Сумма первых пяти членов прогрессии равна -1705.</span>
4/9*3/4*1/3=(4/9*3/4)*1/3=3/1*1/3=1
X+3 1/5= 10 4/5 - 7 2/5
X+3 1/5= 3 2/5
X=3 1/5 - 3 2/5
X=1/5
<em>----------------------------------------</em>
<em><u>1/5+ 3 1/5 = 3 2/5</u></em>