A=x2-4=(x-2)(x+2)
Khi x=102 thì \(A=\left(102-2\right)\left(102+2\right)\)
\(=104\cdot100=10400\)
\(A=x^2-4\)
\(A=x^2-2^2\)
\(A=\left(x-2\right)\left(x+2\right)\)
Thay \(x=102\) vào A ta được:
\(A=\left(102-2\right)\left(102+2\right)\)
\(A=100.104\)
\(A=10400\)