45-58+(-45)+(+58)-3=45-58-45+58-3=(45-45)+(58-58)-3=-3

(-57)-(-12)+3-(-57)=-57+12+3+57=(-57+57)+12+3=15

-(-24)-(-30)+(-24)-30+8=24+30-24-30+8=(24-24)+(30-30)+8=8

-(-12)+(+19)-(+12)+8-19=12+19-12+8-19=(12-12)+(19-19)+8=8

47-(-53)+(-47)-(+53)=47+53-47-53=(47-47)+(53-53)=0

-(+28)+32-(-28)+(-34)=-28+32+28-34=(-28+28)-(34-32)=-2

15-(+72)+(-15)+(+72)=15-72-15+72=(15-15)+(72-72)=0

20-(+46)+(-25)-(-46)=20-46-25+46=(20-25)+(46-46)=-5

28-(-32)+(-28)-32+5=28+32-28-32+5=(28-28)+(32-32)+5=5

-75+(-49)+(+75)+49-12=-75-49+75+49-12=(-75+75)+(49-49)-12=-12

\(...=45-58-45+58-3=-3\)

\(...=-57+12+3+57=15\)

\(...=24+30-24-30+8=8\)

\(...=12+19-12+8-19=8\)

\(...=47+53-47-53=0\)

\(...=-28+32+28-34=-2\)

\(...=15-72-15+72=0\)

\(...=20-46-25+46=-5\)

\(=...28+32-28-32+5=5\)

\(...=-75-49+75+49-12=-12\)

$(48-3.x):5=9$

$48-3.x=9.5$

$48-3.x=45$

$3.x=48-45$

$3.x=3$

$x=3:3$

$x=1$

( 48 - 3 .x ) : 5 = 9

⇒ 48 - 3 . x = 45

⇒ 3 . x = 3

⇒ x = 1

Vậy x = 1.

$11+2.(x-3)=15$

$2.(x-3)=15-11$

$2.(x-3)=4$

$x-3=4:2$

$x-3=2$

$x=2+3$

$x=5$

11 + 2. ( x - 3 ) = 15

⇒  2. ( x -3 ) = 26

⇒ x - 3 = 13

⇒ x = 16 

Vậy x = 16.

\(\left(-\dfrac{7}{12}+\dfrac{5}{8}\right)-\left(-\dfrac{3}{8}+\dfrac{5}{12}\right)\)

\(=-\dfrac{7}{12}+\dfrac{5}{8}-\left(-\dfrac{3}{8}\right)-\dfrac{5}{12}\)

\(=\left(-\dfrac{7}{12}-\dfrac{5}{12}\right)+\left(\dfrac{5}{8}+\dfrac{3}{8}\right)\)

\(=-1+1=0\)

\(\left(-\dfrac{7}{12}+\dfrac{5}{8}\right)-\left(-\dfrac{3}{8}+\dfrac{5}{12}\right)\)

\(=-\dfrac{7}{12}+\dfrac{5}{8}+\dfrac{3}{8}-\dfrac{5}{12}\)

\(=\left(-\dfrac{7}{12}-\dfrac{5}{12}\right)+\left(\dfrac{5}{8}+\dfrac{3}{8}\right)\)

\(=-\dfrac{12}{12}+\dfrac{8}{8}\)

\(=-1+1\)

\(=0\)

$3\times5^{2}=3\times25=75$

\(3\cdot5^2\)

\(=3\cdot25\)

\(=75\)

Đề là $x$ thuộc ước $20$ và $x>8$ phải không nhỉ? Nếu vậy thì bạn tham khảo.

Gọi $A$ là tập hợp của ước $20$

$A={1;2;4;5;10;20}$

Ta có: $20;10>8$

Vậy $x\in{10;20}$

\(x\inƯ\left(20\right)=\left\{1;2;4;5;10;20\right\}\)

Vì: \(x>8\)

=> \(x=\left\{10;20\right\}\)

\(4^3:2^5+3^5:9^2=64:32+243:81=2+3=5\\ \left(\dfrac{1}{2}\right)^5-1,5^2+\dfrac{31}{32}+102,25=\dfrac{1}{32}-\dfrac{9}{4}+\dfrac{31}{32}+\dfrac{409}{4}\\ =\left(\dfrac{1}{32}+\dfrac{31}{32}\right)+\left(\dfrac{409}{4}-\dfrac{9}{4}\right)=1+100=101\\ \left(-1\right)^{2023}+\left(-\dfrac{1}{2}\right)^2:2=\left(-1\right)+\dfrac{1}{4}:2=-1+\dfrac{1}{8}=-\dfrac{7}{8}\)

\(48\div4+3^9\div3^7+5^0\)

\(=12+9+1\)

\(=22\)

\(\left(5^{19}\div5^{17}+3\right)\div7\)

\(=\left(25+3\right)\div7\)

\(=28\div7\)

\(=4\)

\(295-\left(32-2^2\times5\right)^2\)

\(=295-144\)

\(=151\)

\(6^2\div9+50\times2-3^3\times3\)

\(=36\div9+100-27\)

\(=4+100-27\)

\(=100-27\)

\(=73\)

48:4+39:37+50

=48:4+3²+1

=12+9+1=22

(519:517+3):7

=(5²+3):7

=(25+3):7

=28:7=4

295-(31-22.5)2

=295-(31-4.5)²

=295-(31-20)²

=295-11²

=295-121

=174

62:9+50.2-33.3

=36:9+50.2-3⁴

=4+100-81

=23

\(2^{x+3}-2^{x+1}-2^x=40\)

\(\Rightarrow2^x\cdot\left(2^3-2-1\right)=40\)

\(\Rightarrow2^x\cdot5=40\)

\(\Rightarrow2^x=40:5\)

\(\Rightarrow2^x=8\)

\(\Rightarrow2^x=2^3\)

\(\Rightarrow x=3\)

a) Ta có: OA=2cm, OB=5cm

=>AB=OA+OB

=>AB=2+5

=>AB=7cm

Theo đề bài biết BI=1cm mà I thuộc tia BO

=>AI=OB-OA-BI

=>AI=5-2-1

=>AI=2cm

b) Theo câu (a) ta có AI=2cm

Mà OA cũng bằng 2cm

=> OA=AI

=>A là trung điểm của OI

O x A B I