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1) 9 x 10 + 10 x 11 + 11 x 12 + ....+ 2015 x 2016
=9x10x11-8x9x10+10x11x12-9x10x11+...+2015x2016x2017-2014x2015x2013
=2015x2016x2017-8x9x10
=8193537360
a) 20,8 x 45 + 0,37 x 15 + 20,8 x 55 x 0,63
= 20,8 x ( 45 + 55 x 0,63 ) + 0,37 x 15
= 20,8 x ( 45 + 34,65 ) + 5,55
= 20,8 x 79,65 + 5,55
= 1656,72 + 5,55
= 1662,27
b) ( 2013 x 2014 + 2014 x 2015 + 2015 x 2016 ) x ( 1 + 1/3 - 1 và 1/3 )
= ( 2013 x 2014 + 2014 x 2015 + 2015 x 2016 ) x [( 1 - 1 ) + ( 1/3 - 1/3 ) ]
= ( 2013 x 2014 + 2014 x 2015 + 2015 x 2016 ) x 0
= 0
2015 + 2015 x 2 + 2015 x 3 + 2015 x 4 = 2015 x ( 1 + 2 + 3 + 4 )
= 2015 x 10 = 20150
\(\dfrac{x-25-124}{2015}\) + \(\dfrac{x-124-2015}{25}\) + \(\dfrac{x-2015-25}{124}\) = 3
\(\dfrac{x-15-124}{2015}\) - 1 + \(\dfrac{x-124-2015}{25}\) - 1 + \(\dfrac{x-2015-25}{124}\) - 1 = 0
\(\dfrac{x-15-124-2015}{2015}\)+\(\dfrac{x-124-2015-25}{25}\)+\(\dfrac{x-2015-25-124}{124}\) = 0
\(\dfrac{x-\left(15+124+2015\right)}{2015}\)+\(\dfrac{x-\left(124+2015+25\right)}{25}\)+\(\dfrac{x-\left(2015+25+124\right)}{124}\) = 0
(\(x\) - 2164).(\(\dfrac{1}{2015}\)+\(\dfrac{1}{25}\)+\(\dfrac{1}{124}\)) = 0
\(x-2164\) = 0
\(x\) = 2164
Giải:
\(B=\left(5+10+15+...+2015\right)\times\left(20142014\times2015-20152015\times2014\right)\)
\(B=\left(5+10+15+...+2015\right)\times\left(10001\times2014\times2015-10001\times2015\times2014\right)\)
\(B=\left(5+10+15+...+2015\right)\times0\)
\(B=0\)
Chúc em học tốt!
B = (5+10+15+.........+2015) x (20142014 x 2015-20152015 x 2014)
B = (5+10+15+.........+2015) x ( 2014 x 1001 x 2015 - 2015 x 1001 x 2014 ] B = (5+10+15+.........+2015) x 0B = 0 nha
2015 x 23 + 55 x 2015 + 11 x 2015 x 2
= 2015 x (23 + 55 + 11 x 2)
= 2015 x (23 + 55 + 22)
= 2015 x (78 + 22)
= 2015 x 100
= 201500
\(2015x23+55x2015+11x2015x2\)
\(=2015x\left(23+55+11x2\right)\)
\(=2015x\left(23+55+22\right)\)
\(=2015x100\)
\(=201500\)