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Ответ:

[tex]d= a_{n+1}-a_{n} \\a_{n}= a_{1}+d(n-1)[/tex]

1) [tex]d= 10.5 - 8.5 = 2[/tex]

[tex]a_{4} =8.5+2*(4-1) = 8.5+6=14.5\\[/tex]

2) [tex]d= -16-(-19)=3[/tex]

[tex]a_{6}= -19+3*(6-1)=-19+15=-4[/tex]

3) [tex]d=19-23=-4[/tex]

[tex]a_{5}=23+(-4)*(5-1)=23-16=7\\[/tex]

4) [tex]d=-3.7-(-1.7)=-2[/tex]

[tex]a_{7} = -1.7+(-2)*(7-1)=-1.7-12=-13.7[/tex]