We have,
a,b,c are in A.P.
2b=a+c ……. (1)
a,x,b are in G.P.
x2=ab …… (2)
b,y,c are in G.P.
y2=bc ……. (3)
From equation (1) and (2), we get
x2=(2b−c)b
x2=2b2−bc
On putting the value of bc in above expression, we get
x2=2b2−y2
2b2=x2+y2
So, x2,b2,y2 are in A.P.
Hence, proved.