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Áp dụng công thức tính dãy số ta có :
\(164+165+...+1000=\frac{\left[\left(1000-164\right):1+1\right].\left(1000+164\right)}{2}=\frac{837.1164}{2}=487134\)
\(164+165+166+...+1000\)
\(=\frac{\left(\left\{1000+164\right\}.\left[1000-164\right]:1+1\right)}{2}\)
\(=\frac{974268}{2}=487134\)
Câu 3:
Theo đề, ta có;
\(\left\{{}\begin{matrix}4a+2b+c=3\\-\dfrac{b}{2a}=1\\-\dfrac{b^2-4ac}{4a}=2\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}b=-2a\\b^2-4ac=-8a\\4a+2b+c=3\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}b=-2a\\4a^2-4ac=-8a\\4a+2b+c=3\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}b=-2a\\4a\left(a-c\right)=4a\cdot\left(-2\right)\\4a+2b+c=3\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}b=-2a\\c=a+2\\4a-4a+a+2=3\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}a=1\\b=-2\\c=3\end{matrix}\right.\)
Câu 3:
Theo đề, ta có;
\(\left\{{}\begin{matrix}4a+2b+c=3\\-\dfrac{b}{2a}=1\\-\dfrac{b^2-4ac}{4a}=2\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}b=-2a\\b^2-4ac=-8a\\4a+2b+c=3\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}b=-2a\\4a^2-4ac=-8a\\4a+2b+c=3\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}b=-2a\\4a\left(a-c\right)=4a\cdot\left(-2\right)\\4a+2b+c=3\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}b=-2a\\c=a+2\\4a-4a+a+2=3\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}a=1\\b=-2\\c=3\end{matrix}\right.\)
164. It’s a six–hour drive from London to Edinburgh.
It takes ________six hours to drive from London to Edinburgh.____________________________________
165. It’s ages since Alan visited his parents.
Alan _______hasn't visited his parents for ages__________________________________________________
166. Mr. Will lost his job because he was late every day.
If _______Mr. Will hadn't been late every day,he wouldn't have lost his job_________________________________________
167. The police made the youth empty his pocket.
The youth _______was made empty his pocket._______________________________________________
168. Lawrence hasn’t seen his sister since she left for Japan.
Lawrence last ______saw his sister when she left for Japan.___________________________________________
169. John is fat because he eats so many chips.
If ________John didn't eat so many chips,he wouldn't be fat______________________________________________
170. If Joe doesn’t change his way, he will end up in prison.
Unless ________________Joe changes his way, he will end up in prison.___________________________________
171. Having a vacation abroad is interesting.
It’s _________interesting to have a vacation abroad___________________________________________
172. The water was so cold that the children could not take a swim.
The water wasn’t _______warm enough for the children to take a swim. _______________________________________
173. It’s two months since I last spoke to her.
I haven’t _________spoken to her for two months__________
Chiều cao trung bình của đội bóng:
(164 + 165 + 167 + 170 + 171 + 169) : 6 ≈ 167,7 (cm)
166. “Are Tam and Hoa late for class?” Tuan asked Lan
………………………tuan asked lan if tam and hoa were late for class………………
167. She said to me “Can you speak Chinese?”
…………………… she asked if/whether I could speak Chinese…………………
168. “Will she be here for five days?” Tam asked Thu
…………………Tam asked Thu if she would be there for 5 days……………………
169. “Were you reading this book at 8 o’clock last Sunday?” She asked Ba
………………………she asked ba if he had been reading that book at 8 o’clock the previous Sunday………………
