Question

cần phần b thôi ạaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa

Answer 1

\(1.\dfrac{1\times2+2\times3+3\times4+...+20\times21}{1+2-3-4+5+6-7-8+...197+198-199-200+201}\)

\(=\dfrac{1\cdot21}{1+\left(-5\right)+5+\left(-9\right)+9+...+\left(-197\right)+197+\left(-201\right)+201}\)

\(=\dfrac{21}{1+0+0+0+...+0+0}\)

\(=21\)