\(\frac{5}{7}:x=\frac{2}{3}x\frac{3}{4}\)

\(\frac{5}{7}:x=\frac{1}{2}\)

\(x=\frac{5}{7}:\frac{1}{2}\)

\(x=\frac{10}{7}\)

5/7:x=6/12

    x=6/12 : 5/7

   x=42/60

    x=7/10

\(\frac{5}{7}:X=\frac{1}{2}\)

      \(X=\frac{5}{7}:\frac{1}{2}\)

       \(X=\frac{10}{7}\)

Nha bn!!

HT!!!

Bài 1:

123.4=492

145.2=290

420.2=840

Bài 2:

23-14+17+24-13+73=110

2+3+4+5+...+26=350

1.1+2.2+3.3+...+9.9=285

Bài 1:

123.4=492

145.2=290

420.2=840

Bài 2:

23-14+17+24-13+73=110

2+3+4+5+...+26=350

1.1+2.2+3.3+...+9.9=285

\(=\lim\limits\dfrac{n^2+an+2020-n^2}{\sqrt{n^2+an+2020}+n}+\lim\limits\dfrac{n^3-bn^3-6n^2-3n-2021}{n^2+\sqrt[3]{\left(bn^3+6n^2+3n+2021\right)^2}+n\sqrt[3]{bn^3+6n^2+3n+2021}}\)

\(=\lim\limits\dfrac{\dfrac{an}{n}+\dfrac{2020}{n}}{\sqrt{\dfrac{n^2}{n^2}+\dfrac{an}{n^2}+\dfrac{2020}{n^2}}+\dfrac{n}{n}}+\lim\limits\dfrac{\dfrac{\left(1-b\right)n^3}{n^2}-\dfrac{6n^2}{n^2}-\dfrac{3n}{n^2}-\dfrac{2021}{n^2}}{\dfrac{n^2}{n^2}+\dfrac{\sqrt[3]{\left(bn^3+6n^2+3n+2021\right)^2}}{n^2}+\dfrac{n\sqrt[3]{bn^3+6n^2+3n+2021}}{n^2}}\)

\(=\dfrac{1}{2}a+\lim\limits\dfrac{\left(1-b\right)n-6}{1+\sqrt[3]{b^2}+\sqrt[3]{b}}\)

De gioi han bang 0 thi \(\left(1-b\right)=0\Leftrightarrow b=1\Rightarrow\lim\limits\dfrac{\left(1-b\right)n-6}{1+\sqrt[3]{b^2}+\sqrt[3]{b}}=-\dfrac{6}{3}=-2\)

\(\Rightarrow\dfrac{1}{2}a-2=0\Leftrightarrow a=4\)

\(\Rightarrow P=4^{2020}+2^{2021}-1\)

P/s: Tổng này hỏi có bao nhiêu chữ số thì tui còn tìm được, chứ viết hẳn ra thì..chắc nhờ siêu máy tính của nasa :v

a) 

\(\left(1-\dfrac{1}{5}\right)x\left(1-\dfrac{2}{5}\right)x...x\left(1-\dfrac{9}{5}\right)\\ =\left(1-\dfrac{1}{5}\right)x...x\left(1-\dfrac{5}{5}\right)x...x\left(1-\dfrac{9}{5}\right)\\ =\left(1-\dfrac{1}{5}\right)x...x0x...x\left(1-\dfrac{9}{5}\right)=0\)

x là nhân nhé :)) 

b)

\(\dfrac{1}{2}x\dfrac{2}{3}x...x\dfrac{9}{10}\\ =\dfrac{1x2x...x9}{2x3x...x10}=\dfrac{2x3x...x9}{2x3x...x9x10}=\dfrac{1}{10}\)

a) Ta có 1+2+3+4+...+x=210

          => x.(x-1):2=210

          =>x.(x-1)=210.2=420=20.21

          =>x=20

b) Ta có (x+1)+(x+2)+(x+3)+...+(x+99)=6138

          => x.99 +1+2+3+...+99=6138

          =>x.99+4851=6138

          =>x.99=6138-4851=1287

         =>x=1287:99=13

b.(x+1)+(x+2)+...+(x+99)=6138

(x+x+..+x)+(1+2+...+99)=6138

99 x X + a=6138

99 x X=6138 - a

x=(6138- a):99

x=b

a;b là kết quả bn tự tính nha!:>

a) 1 + 2 + 3 + 4 + ....+ x = 210

=> ( x + 1 ) . x : 2 = 210

=> ( x + 1 ) . x = 420

=> ( x + 1 ) . x = 20 x 21

=> x = 20

b) ( x + 1 ) + ( x + 2 ) + ( x + 3 ) + ....+ ( x + 99 ) = 6138

=> ( x + x + x + .... + x ) + ( 1 + 2 + 3 + .... + 99 ) = 6138

=> 99x + ( 1 + 2 + 3 + ...+ 99 ) = 6138

Ta có :

Số số hạng là : ( 99 - 1 ) + 1 = 99

Tổng là : ( 99 + 1 ) . 99 : 2 = 4950

=> 99x + 4950 = 6138

=> 99x = 1188

=> x = 12

1 + 2 x 2 + 3 x 3 + 4 x 4 + 5 x 5 + 6 x 6 + 7 x 7 + 8 x 8 + 9 x 9 + 10 x 10

= 1 + 4 + 9 + 16 + 25 + 36 + 49 + 64 + 81 + 100

= 385

1 + 2x2 + 3x3 + 4x4 + 5x5 + 6x6 + 7x7 + 8x8 + 9x9 + 10x10

= 1+4+9+16+25+36+49+64+81+100

=(81+9)+(64+16)+(49+1)+)36+4)+25+100

=90+80+50+40+25 +100

=385

Đặt T = 1 + 2 x 2 + ... + 10 x 2 = 385