Question

Найти а1 и а6 ,если а3=7,а7=18

Answer 1

$a3 = a1 + 2d = 7 \ a7 = a1 + 6d = 18 \ 4d = 11 \ d = frac{11}{4} \ a1 + 2 times frac{11}{4} = 7 \ a1 = frac{14}{2} - frac{11}{2} \ a1 = frac{3}{2} \ a6 = frac{3}{2} + 5 times frac{11}{4} = frac{6 + 55}{4} = frac{61}{4}$