a) Ta có: \(1990.1990-1992.1998=1990.1990-\left(1990+2\right).\left(1990-2\right)\)
\(=1990.1990-1990.1990+4\)
\(=4\)
b) Ta có: \(\left(2+4+6+...+100\right).\left(36.333-108.111\right)\)
\(=\left(2+4+6+...+100\right).\left(36.3.111-36.3.111\right)\)
\(=\left(2+4+6+...+100\right).0\)
\(=0\)
c) Ta có: \(19991999.1998-19981998.1999\)
\(=10001.1999.1998-10001.1998.1999\)
\(=0\)
a)1990.1999.-19992-19998
= 19990.1990 - (1990+2) . (19990-2)
= 1990.19990+19990.19990+4 = 4
b)(2+4+6+.....+100) . (36.333+108.111)
=(2+4+6+....+100) . 0 = 0