Excel formula where the outcome remains unchanged when values change in future

     A            B            C
1   Area        constant    Land value
2  0.2500       200,000      50,000.00
3  0.3650       200,000      73,000.00
4  1.2540       200,000     250,800.00
5  0.2580       200,000      51,600.00

In the above excel sheet columns C2 to C5 hold the formula =(A2*B2), =(A3*B3), =(A4*B4), =(A5*B5). Help me with a formula where the answers in cells C2, C3, C4 and C5 remain unchanged when values in column A or B change.