1+2+3+4+5+6+7+8+9

=(1+9)+(2+8)+(3+7)+(4+6)+5

=10+10+10+10+5

=10×4+5

=40+5

=45

Học tốt

= (1+9) + (2+8) + ( 3+7 ) + (4+6) + 5

= 10+10+10+10+5

= 10*4+5

=40+5

=45

=( 1+ 9) +( 2+8) +(3+ 7) +(4+ 6) + 5

=10 + 10 + 10 + 10 + 5

=10 x 4 + 5

=45

các bn lm đến đâu cx dc miễn là lm hộ mk cái ạ, ai đang lm vào nhắn tin vs mk để mk bít nha

a; \(-\dfrac{8}{3}+\dfrac{7}{5}-\dfrac{71}{15}< x< -\dfrac{13}{7}+\dfrac{19}{14}-\dfrac{7}{2}\)

              -\(\dfrac{19}{15}\) - \(\dfrac{71}{15}\) < \(x\) < -\(\dfrac{1}{2}\) - \(\dfrac{7}{2}\)

              -6 < \(x\) < -4

             vì \(x\) \(\in\) Z nên \(x\) = -5

- \(\dfrac{19}{6}+\dfrac{-15}{2}+\dfrac{11}{3}\) < \(x\) < - \(\dfrac{5}{4}\) + \(\dfrac{19}{12}\) - \(\dfrac{10}{3}\)

- \(\dfrac{32}{3}+\dfrac{11}{3}< x< \) \(\dfrac{1}{3}\) - \(\dfrac{10}{3}\)

-7 < \(x\) < - 3

Vì \(x\in\) Z nên \(x\in\) {-6;-5;-4}

7⁶ + 7⁵ - 7⁴

= 7⁴( 7² + 7 - 1 )

= 7⁴ . 55

= 7⁴ . 5 . 11 chia hết cho 11

Ta có :

7 ⁶ + 7 ⁵ - 7 ⁴ 

= 7 ⁴ ( 7 ² + 7 - 1 )

= 7 ⁴ . 55

= 7 ⁴ . 5 . 11 chia hết cho 11

Vậy 7 ⁶ + 7 ⁵ - 7 ⁴ chia hết cho 11

a)\(\left(x+8\right)-11=20-15\)

\(\left(x+8\right)-11=5\)

\( x+8=5+11\)

\(x+8=16\)

\(x=8\)

b) \(2x-\left(3+x\right)=5-7\)

\(2x-\left(3+x\right)=-2\)

\(2x-3-x=-2\)

\(x=1\)

c) \( \left(3x-2^4\right)\times7^5=2\times7^6\)

\(3x-2^4=2\times\left(7^6:7^5\right) \)

\(\left(3x-2^4\right)=2\times7^2\)

\(3x-2^4=2\times49\)

\(3x-16=98\)

\(3x=114\)

\(x=38\)

6/7+5/8÷5-3/16×(-2)²

=6/7+1/8-3/4

=55/56-3/4

=13/56

b.2/3 + 1/3.( -4/9 + 5/6 ) : 7/12

   =2/3 + 1/3. ( -8/18 + 15/18 ) : 7/12

    =2/3 + 1/3 . 7/18 : 7/12

      =2/3 + 7/54 : 7/12

      = 2/3 + 2/9

       =6/9 + 2/9

        = 8/9

\(A=\dfrac{1}{3}+\dfrac{1}{4}+\dfrac{1}{4}+\dfrac{1}{5}+\dfrac{1}{5}+\dfrac{1}{6}+\dfrac{1}{6}+\dfrac{1}{7}+\dfrac{1}{7}+\dfrac{1}{8}+\dfrac{1}{8}+\dfrac{1}{9}\)

=1/3+1/2+2/5+1/3+2/7+1/4+1/9

=2789/1260

18 - 10 : ( +2 ) - 7 

= 18 - 5 - 7

= 13 - 7

= 16

( 6 . 8 - 10 : 5 ) + 3 . ( -7 )

= ( 48 - 2 ) + -21

= 46 + ( - 21 )

= 25

( 6 . 8  - 10 : 5 ) + 3 . ( - 7 )

= ( 48 - 2 ) + ( - 21 )

= 46 + ( - 21 )

= 25

\(A=3\sqrt{2}+5\sqrt{8}-2\sqrt{50}\)

\(=3\sqrt{2}+10\sqrt{2}-10\sqrt{2}\)

\(=3\sqrt{2}\)

\(B=\dfrac{1}{3+\sqrt{5}}+\dfrac{1}{3-\sqrt{5}}\)

\(=\dfrac{3-\sqrt{5}}{\left(3+\sqrt{5}\right)\left(3-\sqrt{5}\right)}+\dfrac{3+\sqrt{5}}{\left(3+\sqrt{5}\right)\left(3-\sqrt{5}\right)}\)

\(=\dfrac{3-\sqrt{5}+3+\sqrt{5}}{9-5}\)

\(=\dfrac{3}{2}\)

\(A=3\sqrt{2}+5\sqrt{8}-2\sqrt{50}\)

\(A=3\sqrt{2}+10\sqrt{2}-10\sqrt{2}=3\sqrt{2}\)

\(B=\dfrac{1}{3+\sqrt{5}}+\dfrac{1}{3-\sqrt{5}}\)

\(B=\dfrac{3-\sqrt{5}+3+\sqrt{5}}{9-5}=\dfrac{6}{4}=\dfrac{3}{2}\)

\(C=\sqrt{7-4\sqrt{3}}+\sqrt{12+6\sqrt{3}}\)

\(C=\sqrt{\left(2-\sqrt{3}\right)^2}+\sqrt{\left(3+\sqrt{3}\right)^2}\)

\(C=2-\sqrt{3}+3+\sqrt{3}=5\)