by Math Tutor » Sun Jun 20, 2010 11:48 am
suppose a,b,c are the first three terms of the arithmetic progression
then:
a + b + c = 18
a2 + b2 + c2 = 126
a, b, c form an arithmetic progression so:
a2 = b + c
so we have a system of three equations and 3 variables
from the first and the third we have
a + a2 = 18 - so we know a