\(\Rightarrow\left(\frac{1}{1}-\frac{1}{30}\right)x=-3\)
\(\Rightarrow\frac{29}{30}x=-3\)
\(\Rightarrow x=\left(-\frac{29}{90}\right)\)
tính trog ngoặc trc nè :
\(\frac{1}{1.2.3.4}+\frac{1}{2.3.4.5}+...+\frac{1}{27.28.29.30}\)
=\(\frac{1}{1.2.3}-\frac{1}{2.3.4}+\frac{1}{2.3.4}-\frac{1}{3.4.5}...+\frac{1}{27.28.29}-\frac{1}{28.29.30}\)
=\(\frac{1}{1.2.3}-\frac{1}{28.29.30}\)
=\(\frac{1}{6}-\frac{1}{24360}\)
=\(\frac{1353}{8120}\)
thay vô biểu thức :
\(\frac{1353}{8120}.x=-3\)
x=\(-\frac{8120}{451}\)