Xét x^{2} - (x-1)^{2} = 2x - 1Cho x=2,4,6,8,...,200 \Rightarrow S= 2*2-1+2*4-1+2*6-1+2*8-1+...+2*200-1\Leftrightarrow S=2*(2+4+6+8+...+200)-1*100\Leftrightarrow S=2*\frac{(2+200)*100}{2}-100=10000
Xét
$x^{2} - (x-1)^{2} = 2x - 1
$Cho
$x=2,4,6,8,...,200
$$\Rightarrow S= 2
.2-1+2
.4-1+2
.6-1+2*8-1+...+2
.200-1
$$\Leftrightarrow S=2(2+4+6+8+...+200)-1
.100
$$\Leftrightarrow S=2
.\frac{(2+200)100}{2}-100=10000
$