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bài 1
\(A=\left(\dfrac{3}{8}+\dfrac{1}{4}+\dfrac{5}{12}\right):\dfrac{7}{8}\)
\(A=\dfrac{9+6+10}{24}:\dfrac{7}{8}=\dfrac{25}{24}.\dfrac{8}{7}=\dfrac{25.1}{3.7}=\dfrac{25}{21}\)
\(B=\dfrac{1}{4}:\left(10,3-9,8\right)-\dfrac{3}{4}\)
\(B=\dfrac{1}{4}:\dfrac{1}{2}-\dfrac{3}{4}\)
\(B=\dfrac{1}{4}.2-\dfrac{3}{4}\)
\(B=\dfrac{1}{2}-\dfrac{3}{4}=-\dfrac{1}{4}\)
\(M=-\dfrac{5}{7}.\dfrac{2}{11}+\dfrac{5}{7}.\dfrac{9}{11}+1\dfrac{5}{7}\)
\(M=-\dfrac{5}{7}\left(-\dfrac{2}{11}+\dfrac{9}{11}\right)+1\dfrac{5}{7}\)
\(M=-\dfrac{5}{7}.\dfrac{7}{11}+\dfrac{12}{7}\)
\(M=-\dfrac{5}{11}+\dfrac{12}{7}=\dfrac{97}{77}\)
\(N=\dfrac{6}{7}+\dfrac{5}{8}:5-\dfrac{3}{16}.\left(-2\right)^2\)
\(N=\dfrac{6}{7}+\dfrac{1}{8}-\dfrac{3.4}{16}\)
\(N=\dfrac{6}{7}+\dfrac{1}{8}-\dfrac{3}{4}=\dfrac{6}{7}-\dfrac{5}{8}=\dfrac{13}{56}\)
Bài 1:
a) Nếu n = -2 thì ta có:
A = \(\dfrac{15}{\left(-2\right)-3}\) = \(\dfrac{15}{-5}\) = -3
Nếu n = 0 thì ta có:
A = \(\dfrac{15}{0-3}\) = \(\dfrac{15}{-3}\) = -5
Nếu n = 5 thì ta có:
A = \(\dfrac{15}{5-3}\) = \(\dfrac{15}{2}\)
b) Để A là số nguyên tố thì 15 \(⋮\) n - 3
=> n - 3 \(\in\) Ư(15) = {-15;-5;-3;-1;1;3;5;15}
=> n \(\in\) {-12;-2;0;2;4;6;8;18}
Bài 2:
b) \(\dfrac{\left|x-1\right|-2}{4}=2\)
=> |x - 1| - 2 = 2 . 4
=> |x - 1| - 2 = 8
=> |x - 1| = 8 + 2
=> |x - 1| = 10
=> \(\left[{}\begin{matrix}x-1=10\\x-1=-10\end{matrix}\right.=>\left[{}\begin{matrix}x=10+1\\x=-10+1\end{matrix}\right.=>\left[{}\begin{matrix}x=11\\x=-9\end{matrix}\right.\)
c) \(\dfrac{x}{3}=\dfrac{14}{y}\)
=> x . y = 14 . 3
=> x . y = 42
=> x,y \(\in\) Ư(42) = {-42;-21;-14;-7;-6;-3;-2;-1;1;2;3;6;7;14;21;42}
=>
| x | -42 | -21 | -14 | -7 | -1 | -2 | -3 | -6 | -42 | 1 | 2 | 3 | 6 | 42 | 21 | 3 | 7 |
| y | -1 | -2 | -3 | -6 | -42 | -21 | -14 | -7 | -1 | 42 | 21 | 14 | 7 | 1 | 2 | 14 | 6 |
Câu 5
\(B=\dfrac{5}{2.1}+\dfrac{4}{1.11}+\dfrac{3}{11.2}+\dfrac{1}{2.15}+\dfrac{13}{15.4}\)
⇒ \(7B=\dfrac{5}{2.7}+\dfrac{4}{7.11}+\dfrac{3}{11.14}+\dfrac{1}{14.15}+\dfrac{13}{15.28}\)
\(7B=\dfrac{1}{2}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{11}+\dfrac{1}{11}-\dfrac{1}{14}+\dfrac{1}{14}-\dfrac{1}{15}+\dfrac{1}{15}-\dfrac{1}{28}\)
\(7B=\dfrac{1}{2}-\dfrac{1}{28}\)
\(7B=\dfrac{13}{28}\)
\(B=\dfrac{13}{196}\)
Bài 1:
a) \(\left(-14\right)+\left(-24\right)=\left(-38\right)\)
b) \(25+5.\left(-6\right)=25+\left(-30\right)=\left(-5\right)\)
c) \(\dfrac{3}{4}+\dfrac{-7}{12}=\dfrac{9}{12}+\dfrac{-7}{12}=\dfrac{1}{6}\)
d) \(\dfrac{2}{5}+\dfrac{1}{3}+\dfrac{7}{15}=\dfrac{6+5+7}{15}=1\)
Bài 2:
a) \(11.62+\left(-12\right).11+50.11=11\left(-12+62+50\right)=11.100=1100\)
b)
\(\dfrac{5}{13}+\dfrac{-5}{7}+\dfrac{-20}{41}+\dfrac{8}{13}+\dfrac{-21}{41}\\ \left(\dfrac{5+8}{13}\right)+\left(\dfrac{-21+\left(-20\right)}{41}\right)+\dfrac{-5}{7}\\ =1+\left(-1\right)+\dfrac{-5}{7}\\ =\dfrac{-5}{7}\)
Bài 3:
a) Do \(\widehat{xOy}< \widehat{xOz}\left(40^o< 120^o\right)\) nên tia Oy nằm giữa hai tia Ox và Oz
=> \(\widehat{xOz}=\widehat{xOy}+\widehat{yOz}\)
=> \(\widehat{yOz}=\widehat{xOz}+\widehat{xOy}=120^o-40^o=80^o\)
b) Vì tia Ot là tia đối của tia Ox nên \(\widehat{xOt}=180^o\)
c) Vì Om là tia phân giác của yOz nên yOm = mOz = \(\dfrac{80}{2}\) = 40o
Vì zOm < zOx (40o < 120o) nên tia Om nằm giữa hai tia Oz và Ox
=> xOz = xOm + zOm
=> xOm = xOz - zOm = 120 - 40 = 80o
Vì xOy < xOm (40 < 80) nên tia Oy nằm giữa hai tia Ox và Om.
Vì tia Oy nằm giữa hai tia Ox và Om và xOy = yOm (cùng bằng 40) nên tia Oy là tia phân giác của xOm.
Bài 4:
a) Gọi d = ƯCLN(12n +1; 30n + 2).
Ta có d thuộc ƯC(12n +1; 30n + 2) nên: 12n +1 chia hết cho d và 30n + 2 chia hết cho d.
=> [5(12n+1)-2(30n+2)] chia hết cho d
=> 1 chia hết cho d
Vậy phân số A là phân số tối giản.
b)Bạn tham khảo link này ik, mik mỏi tay rồi: Câu hỏi của Nguyễn Thị Bảo Ngọc - Toán lớp 6 - Học toán với OnlineMath
1,
x =( -12 . ( -3) ) : 2
x = 18
2,
a, -7/9 . 6/11 + (-2/9) = -14/33 + (-2/9) = -64/99
b, -4/7 : 2 = -4/7 . 1/2 = -2/7
c, 115 - (24 - 5. 3) = 115 - ( 24 - 15) = 115 - 9 = 106
d,= -3/7. (5/9 + 4/9) + 17/7 = -3/7 . 1 +17/7 = -3/7 . 17/7 = -51/49
e, ??? mình cx k biết
1. Tìm \(x\):
a) \(\dfrac{x}{5}=\dfrac{5}{6}+\dfrac{-19}{30}\)
\(\dfrac{x}{5}=\dfrac{1}{5}\)
\(\Rightarrow x=1\)
b) \(\dfrac{-5}{6}-x=\dfrac{7}{12}-\dfrac{1}{3}.x\)
\(\dfrac{-5}{6}-\dfrac{7}{12}=x-\dfrac{1}{3}.x\)
\(x-\dfrac{1}{3}.x=\dfrac{-17}{12}\)
\(\dfrac{2}{3}.x=\dfrac{-17}{12}\)
\(x=\dfrac{-17}{12}:\dfrac{2}{3}\)
\(x=\dfrac{-17}{8}\)
c) \(2016^3.2016^x=2016^8\)
\(2016^x=2016^8:2016^3\)
\(2016^x=2016^{8-3}\)
\(2016^x=2016^5\)
\(\Rightarrow x=5\)
d) \(\left(x+\dfrac{3}{4}\right):\dfrac{5}{2}=3\dfrac{1}{2}\)
\(\left(x+\dfrac{3}{4}\right):\dfrac{5}{2}=\dfrac{7}{2}\)
\(\left(x+\dfrac{3}{4}\right)=\dfrac{7}{2}.\dfrac{5}{2}\)
\(x+\dfrac{3}{4}=\dfrac{35}{4}\)
\(x=\dfrac{35}{4}-\dfrac{3}{4}\)
\(x=\dfrac{32}{4}=8\)
e) \(\left(2,8.x-2^5\right):\dfrac{2}{3}=3^2\)
\(\left(2,8.x-2^5\right)=9.\dfrac{2}{3}\)
\(2,8.x-2^5=6\)
\(2,8.x=6+32\)
\(2,8.x=38\)
\(x=38:2,8\)
\(x=\dfrac{95}{7}\)
f) \(\dfrac{4}{7}.x-\dfrac{2}{3}=\dfrac{2}{5}\)
\(\dfrac{4}{7}.x=\dfrac{2}{5}+\dfrac{2}{3}\)
\(\dfrac{4}{7}.x=\dfrac{16}{15}\)
\(x=\dfrac{16}{15}:\dfrac{4}{7}\)
\(x=\dfrac{28}{15}\)
g) \(\left(\dfrac{3x}{7}+1\right):\left(-4\right)=\dfrac{-1}{28}\)
\(\left(\dfrac{3x}{7}+1\right)=\dfrac{-1}{28}.\left(-4\right)\)
\(\dfrac{3x}{7}+1=\dfrac{1}{7}\)
\(\dfrac{3x}{7}=\dfrac{1}{7}-1\)
\(\dfrac{3x}{7}=\dfrac{-6}{7}\)
\(\Rightarrow3x=-6\)
\(x=\left(-6\right):3\)
\(x=-2\)
2. Thực hiện phép tính:
a) \(\dfrac{1}{2}+\dfrac{1}{2}.\dfrac{2}{3}-\dfrac{1}{3}:\dfrac{3}{4}+1\dfrac{4}{5}\)
\(=\dfrac{1}{2}.\left(\dfrac{2}{3}+1\right)-\dfrac{1}{3}:\dfrac{3}{4}+\dfrac{9}{5}\)
\(=\dfrac{1}{2}.\dfrac{5}{3}-\dfrac{1}{3}:\dfrac{3}{4}+\dfrac{9}{5}\)
\(=\dfrac{5}{6}-\dfrac{4}{9}+\dfrac{9}{5}\)
\(=\dfrac{7}{18}+\dfrac{9}{5}\)
\(=\dfrac{197}{90}\)
b) \(\dfrac{7.5^2-7^2}{7.24+21}\)
\(=\dfrac{7.25-7.7}{7.24+7.3}\)
\(=\dfrac{7.\left(25-7\right)}{7.\left(24+3\right)}\)
\(=\dfrac{7.18}{7.27}\)
\(=\dfrac{2}{3}\)
c) \(\dfrac{2}{3}+\dfrac{1}{3}.\left(\dfrac{-4}{9}+\dfrac{5}{6}\right):\dfrac{7}{12}\)
\(=\dfrac{2}{3}+\dfrac{1}{3}.\dfrac{7}{18}:\dfrac{7}{12}\)
\(=\dfrac{2}{3}+\dfrac{7}{54}:\dfrac{7}{12}\)
\(=\dfrac{2}{3}+\dfrac{2}{9}\)
\(=\dfrac{8}{9}\)
Ta có:\(\dfrac{x}{-12}=\dfrac{-3}{x}\)
\(\Rightarrow x.x=-3.\left(-12\right)\)
\(x^2=36\)
Vì \(x\in Z\)\(\Rightarrow x=\pm6\)
bài 4 dễ mà , bạn làm xong rồi gửi cho mik , đễ mik xem có đúng k nhé