if the sum of 4 terms of an AP. is 20.............n sum of their squares is 120...............find the terms!!!!!!!

PLS EXPLAIN!!!!!!!!!!!!!!!

suppose four terms are (a+3x),(a+x),(a-x),(a-3x)

now sum op ap =20=4a;    =>a=5;

sum of squares of ap =120=(a+3x)²+(a+x)²+(a-x)²+(a-3x)²     => x=1 or x=-1,

in either case four nos turn out to be 2, 4, 6, 8.