B₁₀ = b₁ + 9d = 6,4 + 9*0,8 = 6,4 + 7,2 = 13, 6
![S _{10} = \frac{b _{1}+b _{10} }{2}*10= \frac{6,4+13,6}{2}*10= \frac{20}{2} *10= 10*10= 100](https://tex.z-dn.net/?f=S+_%7B10%7D+%3D+%5Cfrac%7Bb+_%7B1%7D%2Bb+_%7B10%7D++%7D%7B2%7D%2A10%3D+%5Cfrac%7B6%2C4%2B13%2C6%7D%7B2%7D%2A10%3D+%5Cfrac%7B20%7D%7B2%7D+%2A10%3D+10%2A10%3D+100++)
(an) -8;-6,5;-5...
a1=-8, a2=-6,5
d=a2-a1=-6,5-(-8)=-6,6+8=1,5
a10=a1+9d=-8+8*1,5=-8+13,5=5,5
S10=(a1+a10)*10:2=(a1+a10)*5
S10=(-8+5,5)*5=-2,5*5=-12,5
Ответ: а10=5,5 S10=-12,5
2x-1=0 3x+2=0
x=1/2 3x=-2
x=-2/3