Cho hình vẽ và Bx// Ny// OZ và góc OBx= 130 độ, góc ONy= 140 độ. Tính góc BON
Trả lời nhanh hộ mik với
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Bài 1 : Gọi số thứ nhất cần tìm là x,số thứ hai cần tìm là y,số thứ ba cần tìm là z. Theo đề bài ta có :
x2 + y2 + z2 = 8125
Mà \(y=\frac{2}{5}x\)=> \(5y=2x\)=> \(\frac{x}{5}=\frac{y}{2}\)(1)
\(y=\frac{3}{4}z\)=> 4y = 3z => \(\frac{y}{3}=\frac{z}{4}\)(2)
Từ (1) và (2) => \(\frac{x}{5}=\frac{y}{2};\frac{y}{3}=\frac{z}{4}\)
+) \(\frac{x}{5}=\frac{y}{2}\Rightarrow\frac{x}{15}=\frac{y}{6}\)
+) \(\frac{y}{3}=\frac{z}{4}\Rightarrow\frac{y}{6}=\frac{z}{8}\)
=> \(\frac{x}{15}=\frac{y}{6}=\frac{z}{8}\)
=> \(\frac{x^2}{15^2}=\frac{y^2}{6^2}=\frac{z^2}{8^2}\)
Áp dụng t/c dãy tỉ số bằng nhau ta có :
\(\frac{x^2}{15^2}=\frac{y^2}{6^2}=\frac{z^2}{8^2}=\frac{x^2+y^2+z^2}{15^2+6^2+8^2}=\frac{8125}{325}=25=5^2\)
=> x2 = 52 . 152 = 752 => x = \(\pm\)75
y2 = 52 . 62 = 302 => y = \(\pm\)30
z2 = 52 . 82 = 402 => z = \(\pm\)40
Bài 2 tự làm
Read the following passage and mark the A, B, C, or D to indicate the correct word or phrase that best fits each of the numbered blanks.
Dan and Jenifer were (26) ___ their wedding. Before the big (27) ___,they bought a (28) ___, house with big trees all around and were busy repairing it - (29) ___ the walls and cleaning the floors. There were a little workshop nearby, Jenifer hung her beautiful white (30) ___ there to keep it clean.
Three days ago before the wedding, while Dan and Jenifer were at his family's home, a wild tornado (31) ___ from nowhere. The tornado missed his family's home, but when Dan drove to his house, it was not there. The trees (32) ___ the neighbor's house were gone. The tornado destroyed (33) ___ everything in the neighborhood. Just one thing was (34) ___ standing- the workshop. When Dan looked inside, he discovered the wedding dress untouched. He called Jenifer, “Your dress is here!“ I think your wedding is meant to be.“ The lucky (35) ___ cried at their wedding. “They're grateful to be here,“ explained a friend.
26) A.planned B.to plan. C.plan. D.planning
27) A.festival B.anniversary C.day D.party
28) A.50-year-old B.50-year-olds C.50-old-year D.50-years-old D. fixed
29) A.fixing. B.to fix. C.fix. D.fixed
30) A.skirt B.wedding dress C.dress D.fixed
31) A. blown B.came out C.flew D.left
32) A.as well B.as well as C.from D.but
33) A.almost B.except C.with D.all
34) A.never B.there C.still D.also
35) A.people B.guests C.couple D.invitees
a) Ta có: \(\frac{8n+5}{4n+1}=\frac{\left(8n+2\right)+3}{4n+1}=2+\frac{3}{4n+1}\)
Để BT nguyên
=> \(\frac{3}{4n+1}\inℤ\)<=> \(4n+1\inƯ\left(3\right)=\left\{\pm1;\pm3\right\}\)
Mà \(4n+1\equiv1\left(mod4\right)\)
=> \(4n+1\in\left\{1;-3\right\}\Rightarrow n\in\left\{0;-1\right\}\)
b) Ta có: \(7^6+7^5-7^4\)
\(=7^4\left(7^2+7-1\right)\)
\(=7^4\cdot55⋮55\)
=> đpcm