bài 1: đỏi các số thập phhan sau thành phân số

a, 0,415 = \(\dfrac{83}{200}\)

0, 25 = \(\dfrac{1}{4}\)

0,125 =\(\dfrac{1}{8}\)

10,3 \(= \dfrac{103}{10}\)

9,8 \(= \dfrac{49}{5}\)

b, 0,75 = \(\dfrac{3}{4}\)

0,6 \(= \dfrac{3}{5}\)

(3,5)² \(= 12,25 =\dfrac{49}{4}\)

0,375 \(=\dfrac{3}{8}\)

0,7 \(=\dfrac{7}{10}\)

9,75 \(=\dfrac{39}{4}\)

3,5 = 35/10

3,5=\(\dfrac{35}{10}=\dfrac{7}{2}\)

tối giản là 7/2

X x 8 + X x 100 + X x 5 + X x 4 = 34 + 200

X x ( 8 + 100 + 5 + 4 )               = 234

X x 117                                      = 234 : 117

X                                                = 2

học tốt

x:0,125+x:0,01+x:0,2+x:0,25=34+200

x:0,125+x:0.01+x:0.2+x:0.25=234

x*8+x*100+x*5+x*4              =234

x*(8+100+5+4)                     =234

x*117                                    =234

x                                            =234:117

x                                            =2

k cho mk nha!

Bài 3:

Khi mắc nối tiếp:

\(R_{tđ}=R_1+R_2+R_3+R_4=5+10+15+20=50\left(\Omega\right)\)

\(I=I_1=I_2=I_3=I_4=\dfrac{U}{R_{tđ}}=\dfrac{20}{50}=0,4\left(A\right)\)

\(\left\{{}\begin{matrix}U_1=I_1.R_1=0,4.5=2\left(V\right)\\U_2=I_2.R_2=0,4.10=4\left(V\right)\\U_3=I_3.R_3=0,4.15=6\left(V\right)\\U_4=I_4.R_4=0,4.20=8\left(V\right)\end{matrix}\right.\)

Khi mắc song song:

\(\dfrac{1}{R_{tđ}}=\dfrac{1}{R_1}+\dfrac{1}{R_2}+\dfrac{1}{R_3}+\dfrac{1}{R_4}=\dfrac{1}{5}+\dfrac{1}{10}+\dfrac{1}{15}+\dfrac{1}{20}=\dfrac{5}{12}\)

\(\Rightarrow R_{tđ}=2,4\left(\Omega\right)\)

\(U=U_1=U_2=U_3=U_4=20V\)

\(\left\{{}\begin{matrix}I_1=\dfrac{U_1}{R_1}=\dfrac{20}{5}=4\left(A\right)\\I_2=\dfrac{U_2}{R_2}=\dfrac{20}{10}=2\left(A\right)\\I_3=\dfrac{U_3}{R_3}=\dfrac{20}{15}=\dfrac{4}{3}\left(A\right)\\I_4=\dfrac{U_4}{R_4}=\dfrac{20}{20}=1\left(A\right)\end{matrix}\right.\)

BÀI 3:

NỐI TIẾP:

a. \(R=R1+R2+R3+R4=5+10+15+20=50\Omega\)

b. \(I=I1=I2=I3=I4=\dfrac{U}{R}=\dfrac{20}{50}=0,4A\left(R1ntR2ntR3ntR4\right)\)

c. \(\left\{{}\begin{matrix}U1=I1.R1=0,4.5=2A\\U2=I2.R2=0,4.10=4A\\U3=I3.R3=0,4.15=6V\\U4=I4.R4=0,4.20=8V\end{matrix}\right.\)

SONG SONG:

a. \(\dfrac{1}{R}=\dfrac{1}{R1}+\dfrac{1}{R2}+\dfrac{1}{R3}+\dfrac{1}{R4}=\dfrac{1}{5}+\dfrac{1}{10}+\dfrac{1}{15}+\dfrac{1}{20}=\dfrac{5}{12}\Rightarrow R=2,4\Omega\)

c. \(U=U1=U2=U3=U4=20V\left(R1\backslash\backslash\mathbb{R}2\backslash\backslash\mathbb{R}3\backslash\backslash R4\right)\)

b. \(\left\{{}\begin{matrix}I1=U1:R1=20:5=4A\\I2=U2:R2=20:10=2A\\I3=U3:R3=20:15=\dfrac{4}{3}A\\I4=U4:R4=20:20=1A\end{matrix}\right.\)

\(a,x+\dfrac{1}{2}=\dfrac{3}{4}\\ x=\dfrac{3}{4}-\dfrac{1}{2}\\ x=\dfrac{1}{2}\\ b,-\dfrac{2}{3}-x=1\\x=-\dfrac{2}{3}-1\\ x=-\dfrac{5}{3}\\ d,\dfrac{1}{4}+\dfrac{3}{4}:x=\dfrac{5}{2}\\ \dfrac{3}{4}:x=\dfrac{5}{2}-\dfrac{1}{4}\\ \dfrac{3}{4}:x=\dfrac{9}{4}\\ x=\dfrac{3}{4}:\dfrac{9}{4}\\ x=\dfrac{1}{3}\\ e,\left(x+\dfrac{1}{4}\right)\cdot\dfrac{3}{4}=-\dfrac{5}{8}\\ x+\dfrac{1}{4}=-\dfrac{5}{8}:\dfrac{3}{4}\\ x+\dfrac{1}{4}=\dfrac{5}{6}\\ x=\dfrac{5}{6}-\dfrac{1}{4}\\ x=\dfrac{7}{12}\)

\(g,\dfrac{x-3}{15}=\dfrac{-2}{5}\\ 5\left(x-3\right)=-30\\ x-3=-6\\ x=-6+3\\ x=-3\\ h,\dfrac{x}{-2}=\dfrac{-8}{x}\\ x^2=16\\ x=\pm\sqrt{16}\\ x=\pm4\\ k,\dfrac{x+2}{3}=\dfrac{x-4}{5}\\ 5\left(x+2\right)=3\left(x-4\right)\\ 5x+10=3x-12\\ 5x-3x=-12-10\\ 2x=-22\\ x=-11\)

\(m,\left(2x-1\right)^2=4\\ \Rightarrow\left[{}\begin{matrix}2x-1=2\\2x-1=-2\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}2x=3\\2x=-1\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}x=\dfrac{3}{2}\\x=-\dfrac{1}{2}\end{matrix}\right.\)

Đánh giá giúp nhá cảm ơn

a: Xét ΔBAC có BD là phân giác

nên AD/AB=DC/BC

=>AD/4=DC/1=(AD+DC)/(4+1)=40/5=8

=>AD=32cm; DC=8cm

b: Kẻ đường cao AH

=>H là trung điểm của BC

=>HB=HC=5cm

Xét ΔAHC vuông tại H có sin C=AH/AC=5/40=1/8

nên góc C=7 độ

\(BD=\dfrac{2\cdot40\cdot10}{40+10}\cdot\dfrac{cos\widehat{B}}{2}\simeq15,97\left(cm\right)\)

x : 1 + x : 0,5 + x : 0,25 + x : 0,125 = 60

=> \(x+x:\frac{5}{10}+x:\frac{25}{100}+x:\frac{125}{1000}=60\)

=> \(x+x\cdot\frac{10}{5}+x\cdot\frac{100}{25}+x\cdot\frac{1000}{125}=60\)

=> \(x+x\cdot2+x\cdot4+x\cdot8=60\)

=> x(1 + 2 + 4 + 8) = 60

=> x.15 = 60

=> x = 4

Bài làm

\(x:1+x:0,5+x:0,25+x:0,125=60\)

\(x:1+x:\frac{5}{10}+x:\frac{25}{100}+x:\frac{125}{1000}=60\)

\(x:\left(1+\frac{1}{2}+\frac{1}{4}+\frac{1}{8}\right)=60\)

\(x:\left(\frac{8}{8}+\frac{4}{8}+\frac{2}{8}+\frac{1}{8}\right)=60\)

\(x:\frac{15}{8}=60\)

\(x=60x\frac{15}{8}\)

\(x=112,5\)

Vậy \(x=112,5\)

x:1 + x:0,5 + x:0,25 + x:0,125 =60
=>x + x:(1/2) + x:(1/4) + x:(1/8) = 60
=>x + x.(2/1) + x.(4/1) + x.(8/1) =60
=>x + 2x + 4x + 8x = 60
=>15x = 60
=>x = 60/5 = 4