Calculation 1 :

\(1\times1=1\) 

\(2\times2=4\)

\(4\times4=6\)

\(5\times5=5\)

\(7\times7=9\)

If the calculation is correct, the calculation will have the following result :

Calculation 2:

\(1\times1=01\)

\(2\times2=04\)

\(4\times4=16\)

\(5\times5=25\)

\(7\times7=49\)

Comparing calculation 1 with calculation 2, we see : calculation 1 has removed all the tens part of the result  of calculation 2 .

Therefore :

With calculation 1 then :

\(9\times9=1\)