The number of pairs of two digit square numbers, the sum or difference of which are also square numbers is
(1) 0
(2) 1
(3) 2
(4) 3


To do:

We have to find the number of pairs of two digit square numbers, the sum or difference of which are also square numbers.

Solution:

Two digit square numbers are $4^2=16, 5^2=25, 6^2=36, 7^2=49, 8^2=64, 9^2=81$.

Let us find the difference and sum between the square numbers.

$81-64=17, 81-49=32, 81-36=45, 81-25=56, 81-16=65$

$64-49=15, 64-36=28, 64-25=39, 64-16=48$

$49-36=13, 49-25=24, 49-16=33$

$36-25=11, 36-16=20$

$25-16=9=3^2$

$16+25=41, 16+36=52, 16+49=65, 16+64=80, 16+81=97$

$25+36=61, 25+49=74, 25+64=89, 25+81=106$

$36+49=85, 36+64=100=10^2, 36+81=117$

$49+64=113, 49+81=130$

$64+81=145$

From the above data we can observe that the sum or difference of the pairs $(25, 16), (36, 64)$ form a perfect square.

There are 2 such pairs.

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Updated on: 10-Oct-2022

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