câu 1
Tìm a,b,c biết : \(\dfrac{a}{19}\)\(\dfrac{b}{12}\)\(\dfrac{c}{7}\)
và b,c =15
Tính bằng cách hợp lý (nếu có)
a) ${A}= \dfrac{15}{12}+ \dfrac{5}{13}+ \dfrac{-3}{12}+ \dfrac{-18}{13}$
b) ${B}= \dfrac{11}{15} \cdot \dfrac{-19}{13}+ \dfrac{-7}{13} \cdot \dfrac{11}{15}$
c) ${C}=2022^{0}-\Big( \dfrac{1}{7}\Big)^5 \cdot 7^5$
a) A = 15/12 + 5/13 + (-3/12) + (-18/13)
= (15/12 - 3/12) + (5/13 - 18/13)
= 1 - 1
= 0
b) B = 11/15 . (-19/13) + (-7/13) . 11/15
= 11/15.(-19/13 - 7/13)
= 11/15 . (-2)
= -22/15
c) C = 2022⁰ - (1/7)⁵ . 7⁵
= 1 - 1/7⁵ . 7⁵
= 1 - 1
= 0
A = [15/12 + (-3/12)] + [5/13 + ( -18/13)]
A = 12/12 + ( -13/13)
A = 1 + (-1)
A = 0
B = 11/15 x [(-19/13) + ( -7/13)]
B = 11/15 x (-26/13)
B = 11/15 x (-2)
B = -22/15
C = 1 - 1 mũ 5
C = 1 - 1
C = 0
a) \(\dfrac{5}{7}\)+\(\dfrac{3}{4}\).\(\dfrac{-11}{2}\)
b) (\(\dfrac{12}{17}\)+\(\dfrac{19}{7}\)) - (\(\dfrac{-5}{17}\)-\(\dfrac{3}{7}\))
c) (0,125)\(^{12}\).(-8)\(^{12}\)-\(\dfrac{45^3}{15^3}\)
d) \(5\dfrac{2}{7}\).(\(-\dfrac{1}{3}\))-\(2\dfrac{2}{7}\).(\(-\dfrac{1}{3}\))
e) \(\dfrac{9^2.9^3}{3^9}\)
\(a,=\dfrac{5}{7}-\dfrac{33}{8}=-\dfrac{191}{56}\\ b,=\left(\dfrac{12}{17}+\dfrac{5}{17}\right)+\left(\dfrac{19}{7}+\dfrac{3}{7}\right)=1+3=4\\ c,=\left(0,125\cdot8\right)^{12}-\left(\dfrac{45}{15}\right)^3=1-3^3=-26\\ d,=\left(-\dfrac{1}{3}\right)\left(5\dfrac{2}{7}-2\dfrac{2}{7}\right)=-\dfrac{1}{3}\cdot3=-1\\ e,=\dfrac{3^4\cdot3^6}{3^9}=3\)
a) -12=\(\dfrac{-12}{1}\)
b) 2,1=\(\dfrac{21}{10}\)
c) -7\(\dfrac{1}{3}\)=\(\dfrac{-22}{3}\)
d) 19%=\(\dfrac{19}{100}\)
a) A = \(\dfrac{19}{9}-\dfrac{-4}{11}-\dfrac{2}{-3}\)
b) B = \(\dfrac{-5}{6}+\dfrac{-7}{12}-\dfrac{1}{-5}\)
c) C = \(\dfrac{-3}{4}+\dfrac{11}{3}-\dfrac{-5}{18}\)
d) D = \(\dfrac{-19}{3}-\dfrac{4}{5}-\dfrac{-2}{3}\)
a: \(A=\dfrac{19}{9}+\dfrac{4}{11}+\dfrac{2}{3}=\dfrac{209}{99}+\dfrac{44}{99}+\dfrac{66}{99}=\dfrac{319}{99}\)
b: \(B=\dfrac{-50}{60}+\dfrac{-35}{60}+\dfrac{12}{60}=\dfrac{-73}{60}\)
c: \(C=\dfrac{-27}{36}+\dfrac{132}{36}+\dfrac{10}{36}=\dfrac{115}{36}\)
d: \(D=\dfrac{-19}{3}+\dfrac{2}{3}-\dfrac{4}{5}=\dfrac{-17}{3}-\dfrac{4}{5}=\dfrac{-85-12}{15}=-\dfrac{97}{15}\)
A=\(\dfrac{7}{19}\).\(\dfrac{8}{11}\) +\(\dfrac{7}{19}\).\(\dfrac{3}{11}\)+\(\dfrac{12}{19}\) Kết quả phép tính là? A.1 B.2 C.3 D.4
Tìm x;
a, \(\dfrac{x}{19}< \dfrac{7}{57}\)
b, \(\dfrac{15}{11}< \dfrac{5}{x}\)
c, 100,1 < x6 + 6x < 111,1
Tìm x: a)\(\dfrac{1}{-x}=-4\) b) \(\dfrac{x+7}{15}\dfrac{-24}{36}\) c)\(\dfrac{x}{-3}=\dfrac{-12}{x}\) d)\(\dfrac{-2}{x-3}=\dfrac{x-3}{-8}\)
a: =>1/x=4
hay x=1/4
b: =>x+7=-10
=>x=-17
c: =>x2=36
=>x=6 hoặc x=-6
d: =>(x-3)2=16
=>x-3=4 hoặc x-3=-4
=>x=7 hoặc x=-1
\(a,\dfrac{1}{-x}=-4\\ \Rightarrow\left(-x\right)\left(-4\right)=1\\ \Rightarrow4x=1\\ \Rightarrow x=\dfrac{1}{4}\\ b,\dfrac{x+7}{15}=\dfrac{-24}{36}\\ \Rightarrow\dfrac{x+7}{15}=\dfrac{-2}{3}\\ \Rightarrow3\left(x+7\right)=-2.15\\ \Rightarrow3x+21=-30\\ \Rightarrow3x=-51\\ \Rightarrow x=-17\)
\(c,\dfrac{x}{-3}=\dfrac{-12}{x}\\ \Rightarrow x.x=\left(-3\right)\left(-12\right)\\ \Rightarrow x^2=36\\ \Rightarrow x=\pm6\)
\(d,\dfrac{-2}{x-3}=\dfrac{x-3}{-8}\\ \Rightarrow\left(x-3\right)\left(x-3\right)=\left(-2\right)\left(-8\right)\\ \Rightarrow\left(x-3\right)^2=16\\ \Rightarrow\left[{}\begin{matrix}x-3=4\\x-3=-4\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}x=7\\x=-1\end{matrix}\right.\)
a.\(\Leftrightarrow4x=1\Leftrightarrow x=\dfrac{1}{4}\)
b.\(\Leftrightarrow\left(x+7\right).36=-360\Leftrightarrow x+7=-10\Rightarrow x=-17\)
c.\(x^2=36\Leftrightarrow x=6;-6\)
d.\(-2.-8=\left(x-3\right)\left(x-3\right)\Leftrightarrow16=x^2-6x+9\Leftrightarrow x^2-6x-7=0\Rightarrow x=7;-1\)
Câu 1. (2 điểm) Tính.
a) $\dfrac{1}{3}+\dfrac{3}{4}-\dfrac{5}{6}$ ;
b) $\dfrac{-2}{3}+\dfrac{6}{5}:\dfrac{2}{3}-\dfrac{2}{15}$ ;
c) $\dfrac{-3}{7}+\dfrac{5}{13}+\dfrac{-4}{7}$ ;
d) $\dfrac{12}{19}+\dfrac{-8}{13}-\dfrac{12}{19}+\dfrac{5}{-13}+2$ .
a) \(\frac{1}{3}+\frac{3}{4}-\frac{5}{6}\)
\(=\frac{1}{3}+\frac{3}{4}+\frac{-5}{6}\)
\(=\frac{1.4+3.3+\left(-5\right).2}{12}\)
\(=\frac{4+9+\left(-10\right)}{12}\)
\(=\frac{3}{12}\)
\(=\frac{1}{4}\)
b) \(\frac{-2}{3}+\frac{6}{5}\div\frac{2}{3}-\frac{2}{15}\text{ }\)
\(=\frac{-2}{3}+\frac{6}{5}\times\frac{3}{2}-\frac{2}{15}\)
\(=\frac{-2}{3}+\frac{18}{10}-\frac{2}{15}\)
\(=\frac{-2}{3}+\frac{9}{5}+\frac{-2}{15}\)
\(=\frac{\left(-2\right).5+9.3+\left(-2\right)}{15}\)
\(=\frac{\left(-10\right)+27+\left(-2\right)}{15}\)
\(=\frac{15}{15}\)
\(=1\)
c) \(\frac{-3}{7}+\frac{5}{13}+\frac{-4}{7}\text{ }\)
\(=\left(\frac{-3}{7}+\frac{-4}{7}\right)+\frac{5}{13}\)
\(=\frac{-7}{7}+\frac{5}{13}\)
\(=-1+\frac{5}{13}\)
\(=\frac{-13}{13}+\frac{5}{13}\)
\(=\frac{-8}{13}\)
Bài 1 : Thực hiện phép tính
a) \(\dfrac{19}{12}\) + | \(\dfrac{-5}{2}\) | + ( \(\dfrac{3}{2}\) )2
b) \(\dfrac{2}{11}\) . \(\dfrac{16}{9}\) - \(\dfrac{2}{11}\) . \(\dfrac{7}{9}\)
Bài 2 : Tìm x , biết
\(\dfrac{a}{8}\) = \(\dfrac{b}{3}\) và a - b = 55
Bài 1:
a) \(\dfrac{19}{12}+\left|\dfrac{-5}{2}\right|+\left(\dfrac{3}{2}\right)^2=\dfrac{19}{12}+\dfrac{5}{2}+\dfrac{9}{4}\)
\(=\dfrac{19+5.6+9.3}{12}=\dfrac{76}{12}=\dfrac{19}{3}\)
b) \(\dfrac{2}{11}.\dfrac{16}{9}-\dfrac{2}{11}.\dfrac{7}{9}=\dfrac{2}{11}\left(\dfrac{16}{9}-\dfrac{7}{9}\right)=\dfrac{2}{11}.1=\dfrac{2}{11}\)
Bài 2:
Áp dụng t/c dtsbn:
\(\dfrac{a}{8}=\dfrac{b}{3}=\dfrac{a-b}{8-3}=\dfrac{55}{5}=11\)
\(\Rightarrow\left\{{}\begin{matrix}x=11.8=88\\b=11.3=33\end{matrix}\right.\)