53.
If
are in A.P., then prove that
are in A.P.

will be in A.P.
if

will be in A.P. (By adding 1 to each number)
if

will be in A.P.
if

will be in A.P. (By dividing each number a + b + c)
if

if

if

if (b - a) (b + a) = (c - b) (c + b)
if

if

are in A.P. which is true.
Hence,

are in A.P.
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