Độ dài đoạn thẳng BC là:

\(6\times2=12\left(dm\right)\)

Độ dài đoạn thẳng CD là:

\(12\times3=36\left(dm\right)\)

Độ dài đường gấp khúc ABCD là:

\(6+12+36=54\left(dm\right)\)

Đáp số: \(54dm\)

\(910+920+930+940+950+960+970+980+990+1000\)

\(=\left(910+990\right)+\left(920+980\right)+\left(930+970\right)+\left(940+960\right)+\left(950+1000\right)\)

\(=1900+1900+1900+1900+1950\)

\(=7600+1950\)

\(=9550\)

\(129+291+284+298+292+896\)

\(=\left(129+291\right)+\left(284+896\right)+\left(298+292\right)\)

\(=420+1180+590\)

\(=1600+590\)

\(=2190\)

\(120+130+140+150+160+170+180+190\)

\(=\left(120+180\right)+\left(130+170\right)+\left(140+160\right)+\left(150+190\right)\)

\(=300+300+300+340\)

\(=1240\)

\(\sqrt{4x-5}=\sqrt{3}\left(ĐKXĐ:x\ge\dfrac{5}{4}\right)\)

\(\Rightarrow4x-5=3\)

\(\Leftrightarrow4x=8\)

\(\Leftrightarrow x=2\left(tm\right)\)

Vậy \(S=\left\{2\right\}\)

\(579\times y+421\times y=2100\)

\(\left(579+421\right)\times y=2100\)

\(1000\times y=2100\)

\(y=2100:1000\)

\(y=2,1\)

z hả bà, cố gắng thi tốt nhen