Question

find x if 10,x-1,15 are in H.P

Answer 1

if a,b,c,in H.p.
then
b = 2ac/a+c

so

x-1 = 2.10.15/10+15

x-1 = 12

x =13

Answer 2

if a,b,x in H.p then,
we must
b=2ac/a+c
so we can
x-1=2.10.15/10+15
we got
x-1=12
we got an amazing answer
x=13.