Question

calculati folosind factorul comul; 3x1993+1993x1995-1998x1991, 2014x2013+2x2014-2015x2012, 1111+2222+3333+......+9999

Answer 1

3*1993+1993*1995-1998*1991=
=1993(3+1995) - 1998*1991=
=1993 *1998 -1998*1991=
=1998 (1993*1991)=
=1998*2=3996

2014*2013+2*2014-2015*2012=
=2014(2013+2) -2015*2012=
=2014*2015 - 2015*2012=
=2015 (2014-2012)=
=2015*2= 4030

1111+...+9999=
=1111(1+2+...+9)= folosim formula lui Gaus 1+2+3+...+n=n(n+1)/2
=1111*9 *10/2=
=9999*5=
=49995