Question

Дано арифметичну прогресію(an), a6=19, a14=3, знайти а1, d​

Answer 1

Ответ:

а14=а6+8д -> 3=19+8d -> 8д=-16 --> д=-2 а1=31

Answer 2

$\left \{ {{a_{14}=3 } \atop {a_{6}=19 }} \right.\\\\-\left \{ {{a_{1}+13d=3 } \atop {a_{1}+5d=19 }} \right.\\ -------\\8d=-16\\\\\boxed{d=-2}\\\\a_{1}=19-5d=19-5*(-2)=19+10=29\\\\\boxed{a_{1} =29}$