\(\left(2x+1\right)^{10}=49^5\)

\(\left(2x+1\right)^{10}=\left(7^2\right)^5\)

\(\left(2x+1\right)^{10}=7^{10}\)

\(\left(2x+1\right)^{10}=7^{10}\) hoặc \(\left(2x+1\right)^{10}=\left(-7\right)^{10}\)

\(2x+1=7\) hoặc \(2x+1=-7\)

*) \(2x+1=7\)

\(2x=6\)

\(x=3\)

*) \(2x+1=-7\)

\(2x=-8\)

\(x=-4\)

Vậy \(x=-4;x=3\)

(2x +1)¹⁰ = 49⁵

(2x+1)¹⁰ = (7²)⁵

(2x +1)¹⁰ = 7¹⁰

\(\left[{}\begin{matrix}2x+1=7\\2x+1=-7\end{matrix}\right.\)

\(\left[{}\begin{matrix}2x=6\\2x=-8\end{matrix}\right.\)

\(\left[{}\begin{matrix}x=3\\x=-4\end{matrix}\right.\)

a) <=>80-x+6=9.8
    <=>86-x=72
    <=>x=14
b) <=>495-5x-20=10
    <=>475-5x=10
    <=>5x=465
    <=>x=93

\(\frac{1}{1\times10}+\frac{1}{2\times15}+\frac{1}{3\times20}+...+\frac{1}{98\times495}+\frac{1}{99\times500}\)

\(=\frac{1}{1\times2\times5}+\frac{1}{2\times3\times5}+\frac{1}{3\times4\times5}+...+\frac{1}{98\times99\times5}+\frac{1}{99\times100\times5}\)

\(=\frac{1}{5}\times\left(\frac{1}{1\times2}+\frac{1}{2\times3}+\frac{1}{3\times4}+...+\frac{1}{98\times99}+\frac{1}{99\times100}\right)\)

\(=\frac{1}{5}\times\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{98}-\frac{1}{99}+\frac{1}{99}-\frac{1}{100}\right)\)

\(=\frac{1}{5}\times\left(1-\frac{1}{100}\right)=\frac{1}{5}\times\frac{99}{100}=\frac{99}{500}\)

\(\frac{1}{1\times10}+\frac{1}{2\times15}+\frac{1}{3\times20}+...+\frac{1}{98\times495}+\frac{1}{99\times500}\)

\(=\frac{1}{1\times2\times5}+\frac{1}{2\times3\times5}+\frac{1}{3\times4\times5}+...+\frac{1}{98\times90\times5}+\frac{1}{90\times100\times5}\)

\(=\frac{1}{5}\times\left(\frac{1}{1\times2}+\frac{1}{2\times3}+\frac{1}{3\times4}+...+\frac{1}{98\times99}+\frac{1}{99\times100}\right)\)

\(=\frac{1}{5}\times\left(\frac{2-1}{1\times2}+\frac{3-2}{2\times3}+...+\frac{99-98}{98\times99}+\frac{100-99}{99\times100}\right)\)

\(=\frac{1}{5}\times\left(\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{98}-\frac{1}{99}+\frac{1}{99}-\frac{1}{100}\right)\)

\(=\frac{1}{5}\times\left(1-\frac{1}{100}\right)=\frac{99}{500}\)

cảm ơn bạn Xyz và bạn Đoàn Đức Hà nhìu (^-^) thank you !!!!!!!!!!!!!!!!!

đáp án:

505 + 495 = 1000

100 . 10 = 1000

chúc bạn học tốt !!!

=1000

=1000

\(505+495=1000\)

\(100\times10=1000\)

_Chúc bạn học tốt_

a)    1 + 2 + 3 + ....... + x = 1275

<=> ( x + 1 ) . x : 2 = 1275

        ( x + 1 ) . x   = 1275 .2

          ( x + 1 ) . x = 2550

           ( x + 1 ) . x = 51 . 50

          ( x + 1 ) . x = ( 50 + 1 ) . 50

<=> x = 50

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

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

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

                                       99x + 4950 = 6138

                                          99x          = 1188

                                                  x      = 1188 : 99

                                                  x      = 12

c)    x . 1 + x . 2 + ......... + x . 99 = 495

             x. ( 1 + 2 + ...... + 99 ) = 495

              x . 4950 = 495

              x            = 495 : 4950

                 x         = 1/10

Đáp án cần chọn là: A

a: Ta có: \(x\left(2x-3\right)-\left(2x-1\right)\left(x+5\right)=17\)

\(\Leftrightarrow2x^2-3x-2x^2-10x+x+5=17\)

\(\Leftrightarrow-12x=12\)

hay x=-1

-2x(x + 3) + x(2x - 1) = 10

-2x² - 6x + 2x² - x = 10

-7x = 10

x = -10/7