a) ĐKXĐ:

x³ - 1 khác 0

x khác 1

b) A = (5x² + 5x + 5)/(x³ - 1)

= 5(x² + x + 1)/[(x - 1)(x² + x + 1)]

= 5/(x - 1)

Thay x = 7 vào A, ta được:

A = 5/(7 - 1)

= 5/6

A

C

C

B

B

Câu 1.

Công suất của bếp điện:

\(P=\dfrac{U^2}{R}=\dfrac{220^2}{48,4}=1000W\)

Câu 2.

a)Đổi: \(341mA=341\cdot10^{-3}A\)

   Điện trở đèn: \(R=\dfrac{U}{I}=\dfrac{220}{341\cdot10^{-3}}\approx645,16\Omega\)

   Công suất đèn: \(P=U.I=220\cdot341\cdot10^{-3}=75,02W\)

b)Điện năng tiêu thụ của đèn:  \(A=UIt=Pt=75,02\cdot30\cdot4\cdot3600=32408640J=9,0024kWh\)

Số đếm tương ứng của công tơ điện là 9,0024 số điện.

Bài 2 tính công thực hiện của bạn nhân 4 chứ không phải nhân 24 nhé. 

a: \(\frac13-2\frac56+\frac{12}{9}\)

\(=\frac13+\frac43-\frac{17}{6}\)

\(=\frac53-\frac{17}{6}=\frac{10}{6}-\frac{17}{6}=-\frac76\)

b: \(\frac12\cdot\frac56+\frac23\cdot\frac34\)

\(=\frac{5}{12}+\frac{6}{12}=\frac{5+6}{12}=\frac{11}{12}\)

c: \(\left(-\frac37+\frac14\right):\frac{15}{28}\)

\(=\left(-\frac{12}{28}+\frac{7}{28}\right)\cdot\frac{28}{15}\)

\(=-\frac{5}{15}=-\frac13\)

d: \(\frac23-\left(-\frac15\right)-\frac{4}{15}\)

\(=\frac23+\frac15-\frac{4}{15}\)

\(=\frac{10}{15}+\frac{3}{15}-\frac{4}{15}=\frac{9}{15}=\frac35\)

e: \(-\frac{3}{16}\cdot\frac{8}{15}+\frac{-3}{16}\cdot\frac{7}{15}-\frac{5}{16}\)

\(=-\frac{3}{16}\left(\frac{8}{15}+\frac{7}{15}\right)-\frac{5}{16}\)

\(=-\frac{3}{16}-\frac{5}{16}=-\frac{8}{16}=-\frac12\)

f: \(-\frac{20}{23}+\frac23-\frac{3}{23}+\frac25+\frac{7}{15}\)

\(=\left(-\frac{20}{23}-\frac{3}{23}\right)+\frac{10}{15}+\frac{6}{15}+\frac{7}{15}\)

\(=-\frac{23}{23}+\frac{23}{15}=-1+\frac{23}{15}=\frac{8}{15}\)

g: \(\frac57\cdot\frac{5}{11}+\frac57\cdot\frac{2}{11}-\frac57\cdot\frac{14}{11}\)

\(=\frac57\left(\frac{5}{11}+\frac{2}{11}-\frac{14}{11}\right)\)

\(=\frac57\cdot\left(-\frac{7}{11}\right)=-\frac{5}{11}\)

h: \(-\frac57\cdot\frac{3}{13}-\frac57\cdot\frac{10}{13}+1\frac57\)

\(=-\frac57\left(\frac{3}{13}+\frac{10}{13}\right)+1+\frac57\)

\(=-\frac57+1+\frac57=1\)

i: \(\frac74\cdot\frac{29}{5}-\frac75\cdot\frac94+3\frac{2}{13}\)

\(=\frac74\cdot\left(\frac{29}{5}-\frac95\right)+3+\frac{2}{13}\)

\(=\frac74\cdot4+3+\frac{2}{13}=10+\frac{2}{13}=\frac{132}{13}\)

P6:

1. big

2. been

3. bought

4. people

P7:

1. T

2. F

3. F

4. F

P6:

1. biggest

a: \(=\dfrac{1}{3}-\dfrac{17}{6}+\dfrac{4}{3}=\dfrac{5}{3}-\dfrac{17}{6}=\dfrac{10-17}{6}=\dfrac{-7}{7}\)

b: \(=\dfrac{5+6}{12}=\dfrac{11}{12}\)

c: \(=\dfrac{-12+7}{28}\cdot\dfrac{28}{15}=\dfrac{-5}{15}=\dfrac{-1}{3}\)

d: \(=\dfrac{2}{3}+\dfrac{1}{5}-\dfrac{4}{15}=\dfrac{10+3-4}{15}=\dfrac{9}{15}=\dfrac{3}{5}\)

e: \(=\dfrac{-3}{16}\left(\dfrac{8}{15}+\dfrac{7}{15}\right)-\dfrac{5}{16}=\dfrac{-3-5}{16}=\dfrac{-1}{2}\)

f: \(=\dfrac{-20}{23}-\dfrac{2}{23}+\dfrac{2}{3}+\dfrac{2}{5}+\dfrac{7}{15}\)

\(=-1+\dfrac{10+6+7}{15}=\dfrac{-15+23}{15}=\dfrac{8}{15}\)

g: =5/7(5/11+2/11-14/11)

=-7/11*5/7=-5/11

h: =-5/7(10/13+3/13)+1+5/7

=-5/7+1+5/7

=1

i: \(=\dfrac{7}{4}\left(\dfrac{29}{5}-\dfrac{9}{5}\right)+3+\dfrac{2}{13}=7+3+\dfrac{2}{13}=10+\dfrac{2}{13}=\dfrac{132}{13}\)

a, \(2\sqrt{3}-\sqrt{4+x^2}=0\Leftrightarrow\sqrt{4+x^2}=2\sqrt{3}\)

\(\Leftrightarrow x^2+4=12\Leftrightarrow x^2=8\Leftrightarrow x=\pm2\sqrt{2}\)

b, \(\sqrt{16x+16}-\sqrt{9x+9}=0\)ĐK : x >= -1 

\(\Leftrightarrow4\sqrt{x+1}-3\sqrt{x+1}=0\Leftrightarrow\sqrt{x+1}=0\Leftrightarrow x+1=0\Leftrightarrow x=-1\)

c, \(\sqrt{4\left(x+2\right)^2}=8\Leftrightarrow2\left|x+2\right|=8\Leftrightarrow\left|x+2\right|=4\)

TH1 : \(x+2=4\Leftrightarrow x=2\)

TH2 : \(x+2=-4\Leftrightarrow x=-6\)

c: Ta có: \(\sqrt{4\left(x+2\right)^2}=8\)

\(\Leftrightarrow\left|x+2\right|=4\)

\(\Leftrightarrow\left[{}\begin{matrix}x+2=4\\x+2=-4\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=2\\x=-6\end{matrix}\right.\)