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Ta có :
\(\frac{x+2}{11}+\frac{x+2}{12}+\frac{x+2}{13}=\frac{x+2}{14}+\frac{x+2}{15}\)
\(\Rightarrow\frac{x+2}{11}+\frac{x+2}{12}+\frac{x+2}{13}-\frac{x+2}{14}-\frac{x+2}{15}=0\)
\(\Rightarrow\left(x+2\right).\left(\frac{1}{11}+\frac{1}{12}+\frac{1}{13}-\frac{1}{14}-\frac{1}{15}\right)=0\)
\(\Rightarrow x+2=0\left(\text{do }\frac{1}{11}+\frac{1}{12}+\frac{1}{13}-\frac{1}{14}-\frac{1}{15}\ne0\right)\)
\(\Rightarrow x=-2\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(2^{225}=\left(2^3\right)^{75}=8^{75}\)
\(3^{150}=\left(3^2\right)^{75}=9^{75}\)
\(8^{75}< 9^{75}\Rightarrow2^{225}< 3^{150}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 2 ; 2 ; 3 ; 4 phần tự luận bạn tham khảo ở Câu hỏi của Phùng minh long - Toán lớp 7 - Học trực tuyến OLM nhé !
Bài 1 :
\(1)\frac{11}{24}-\frac{5}{41}+\frac{13}{24}+0,5-\frac{36}{41}\)
\(\Rightarrow\left(\frac{11}{24}+\frac{13}{24}\right)-\left(\frac{5}{41}+\frac{36}{41}\right)+\frac{1}{2}\)
\(\Rightarrow1-1+\frac{1}{2}=\frac{1}{2}\)
\(2)\frac{15}{34}+\frac{7}{21}+\frac{19}{34}-1\frac{15}{17}+\frac{2}{3}\)
\(=\frac{15}{34}+\frac{7}{21}+\frac{19}{34}-1-\frac{15}{17}+\frac{14}{21}\)
\(=\left(\frac{15}{34}+\frac{19}{34}-1\right)+\left(\frac{7}{21}+\frac{14}{21}\right)-\frac{15}{17}\)
\(=1-\frac{15}{17}=\frac{2}{17}\)
\(3)1\frac{4}{23}+\frac{5}{21}-\frac{4}{23}+0,5+\frac{16}{21}\)
\(=\left(1\frac{4}{23}-\frac{4}{23}\right)+\left(\frac{5}{21}+\frac{16}{21}\right)+0,5\)
\(=1+1+0,5=2,5\)
\(4)\left(-12\right):\left(\frac{3}{4}-\frac{5}{6}\right)^2\)
\(=\left(-12\right):\left(\frac{-1}{12}\right)^2\)
\(=\left(-12\right).12^2=-12^3\)
\(5)\left(\frac{9}{25}-2.18\right):\left(3\frac{4}{5}+0,2\right)\)
\(=\frac{-891}{25}:4=\frac{-891}{100}\)
\(6)\left(-6,5\right).5,7+5,7.\left(-3,5\right)\)
\(=\left[\left(-6,5\right)+\left(-3,5\right)\right].5,7\)
\(=-10.5,7=57\)
\(7)-3,75.\left(-7,2\right)+2,8.3,75\)
\(=3,75.7,2+2,8.3,75\)
\(=3,75.\left(7,2+2,8\right)\)
\(=3,75.10=37,5\)
\(8)23\frac{1}{4}.\frac{7}{5}-13\frac{1}{4}:\frac{5}{7}\)
\(=23\frac{1}{4}.\frac{7}{5}-13\frac{1}{4}.\frac{7}{5}\)
\(=\left(23\frac{1}{4}-13\frac{1}{4}\right).1,4\)
\(=10.1,4=14\)
\(9)16\frac{2}{7}:\left(\frac{-3}{5}\right)+28\frac{2}{7}:\frac{3}{5}\)
\(=-16\frac{2}{7}:\frac{3}{5}+28\frac{2}{7}:\frac{3}{5}\)
\(=-16\frac{2}{7}.\frac{5}{3}+28\frac{2}{7}.\frac{5}{3}\)
\(=\left(-16\frac{2}{7}+28\frac{2}{7}\right).\frac{5}{3}\)
\(=12.\frac{5}{3}=20\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Ta có Ax // zc
Suy ra góc xAc=C1=40(So le trong)
Lại có By // zc
Suy ra góc cBy=C2=60(so le trong)
Vì góc ACB=C1+C2
Mà C1=40,C2=60
Suy ra góc ACB=40+60=100
Vậy góc ACB=100
Good luck!
![](https://rs.olm.vn/images/avt/0.png?1311)