Question

арифметическая прогрессия
срочнооо

Answer 1

$\left \{ {{a_1+a_6=26} \atop {a_2+a_3=18}} \right. \left \{ {{a_1+a_1+5d=26} \atop {a_1+d+a_1+2d=18}} \right. \left \{ {{2a_1+5d=26} \atop {2a_1+3d=18}} \right. \\ 2a_1+5d-2a_1-3d=26-18 \\ 2d=8 \\ d =4 \\ 2a_1+3d=18 \\ 2a_1+12=18 \\ 2a_1 = 4 \\ a_1 = 2$