Question

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Answer 1

Răspuns:

Explicație pas cu pas:

Answer 2

$\it a_1+a_7=42 \Rightarrow a_1 + a_1+6r=42 \Rightarrow 2a_1+6r=42|_{:2} \Rightarrow a_1+3r=21\ \ \ \ (1) \\ \\ \\ a_{10}-a_3=21 \Rightarrow a_1+9r-a_1-2r=21 \Rightarrow 7r=21 \Rightarrow r=3 \ \ \ \ \ \ \ (2)\\ \\ \\ (1),\ (2) \Rightarrow a_1+9=21|_{-9} \Rightarrow a_1=12$