= ( -2 + 4) + ( -6 +8) + ...+(-18 + 20 )
= 2+2+2+2+2
= 10
= [-2 + 4] + [-6+8] + ... +[-18 + 20]
= 2 + 2 + ... + 2
= 10
= ( -2 + 4) + ( -6 +8) + ...+(-18 + 20 )
=2+2+2+2+2
=10
k mik nhoa
\(\left(-2\right)+4+\left(-6\right)+8+\left(-10\right)+12+\left(-14\right)+16+\left(-18\right)+20\)
\(=\left[\left(-2\right)+\left(-18\right)\right]+\left(4+16\right)+\left[\left(-6\right)+\left(-14\right)\right]+\left(8+12\right)+\left[\left(-10\right)+20\right]\)
\(=\left(-20\right)+20+\left(-20\right)+20+10\)
\(=\left[\left(-20\right)+20\right]+\left[\left(-20\right)+20\right]+10\)
\(=0+0+10\)
\(=10\)