Respuesta :

mirai123

Answer:

[tex]a_1=15[/tex]

Step-by-step explanation:

We are talking about arithmetic progression.

Using the formula:

[tex]a_n=a_1+(n-1) \cdot d[/tex]

[tex]a_7=a_1+(7-1) \cdot d[/tex]

[tex]3=a_1+(7-1) \cdot (-2)[/tex]

[tex]3=a_1+(6) \cdot (-2)[/tex]

[tex]3=a_1-12[/tex]

[tex]a_1=15[/tex]

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Answer:

[tex]\huge \boxed{a_1=15 }}[/tex]

Step-by-step explanation:

Using the nth term formula:

[tex]a_n=a_1+dn-d[/tex]

[tex]a_7=3 \\ \\ n=7 \\ \\ d=-2[/tex]

[tex]3=a_1+-2(7)-(-2)[/tex]

Simplifying and solving for the first term.

[tex]3=a_1-14+2[/tex]

[tex]3=a_1-12[/tex]

[tex]15=a_1[/tex]

The first term of the sequence is 15.

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