Question

А арифмитической прогрессии а3=7,5иа7=14,3 найдите dи а1

Answer 1

a7 = a3+4d
d = (a7-a3):4 = (14,3-7,5):4 = 6,8:4 = 1,7
a3 = a1+2d
a1 = a3-2d = 7,5-2*1,7 = 7,5-3,4 = 4,1

Answer 2

a3=a1+2d=7.5⇒a1=7.5-2d
a7=a1+6d=14.3⇒a1=14.3-6d
7.5-2d=14.3-6d
4d=6.8
d=1.7
a1=7.5-2*1.7=7.5-3.4=4.1