a4=7
a7=-2
a1=?
a9=?
an=a1+d(n-1)
a7=a4+3d
-2=7+3d
-9=3d
d=-3
a4=a1+3d
a1=a4-3d
a1=7-(-9)=16
a9=a7+2d
a9=-2+2*(-3)=-8
Ответ:
a1=16
a9=-8
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Answers & Comments
a4=7
a7=-2
a1=?
a9=?
an=a1+d(n-1)
a7=a4+3d
-2=7+3d
-9=3d
d=-3
a4=a1+3d
a1=a4-3d
a1=7-(-9)=16
a9=a7+2d
a9=-2+2*(-3)=-8
Ответ:
a1=16
a9=-8