B = 99 - 97 + 95 - 93 + 91 - 89 + ... + 7 - 5 + 3 - 1

B = 2 + 2 + 2 + ... + 2 + 2

B = 2 . 50

B = 100

Nhầm 

B = 99 - 97 + 95 - 93 + 91 - 89 + ... + 7 - 5 + 3 - 1

Số số hạng : ( 99 - 1 ) : 2 + 1 = 50 số

Số cặp : 50 : 2 = 25 cặp

Giá trị mỗi cặp : 2 

=> B = 99 - 97 + 95 - 93 + 91 - 89 + ... + 7 - 5 + 3 - 1

= 2 . 25 = 50

\(\frac{1}{2}x-\frac{2}{3}x=\frac{5}{12}\Leftrightarrow\frac{-1}{3}x=\frac{5}{12}\Leftrightarrow x=-\frac{5}{4}\)

99 - 97 + 95 - 93 + 91 - 89 + ... + 7 - 5

= ( 99 - 97 ) + ( 95 - 93 ) + ( 91 - 89 ) + ... + ( 7 - 5 )

= 2 + 2 + 2 + ... + 2

Dãy số trên có số cặp là :

       [ ( 99 - 5 ) : 2 + 1 ] : 2 = 24 ( cặp )

\(\Rightarrow\) 2 . 24 = 48

Vậy phép tính trên = 48 .

- Giúp mình với 

C = 98 + 96 + 94 + .. + 4 + 2 - 97 - 95 - 93 - .. - 3

    = (98 + 96 + 94 + ... + 4 + 2) - (97 + 95 + 93 + ... + 3)

    = 49 . 100 : 2 - 48.100 : 2

    = 49.50 - 48.50

    = 50.(49 - 48)

    = 50 . 1

    = 50

Vậy C = 50

\(C=98+96+94+...+4+2-97-95-93-...-3\)

\(=\left(98+2\right).49:2-\left(97+95+93+...+3\right)\)

\(=49.50-\left(97+3\right).48:2=49.50+48.50=\left(49+48\right).50=97.50=4850\)

`(3x-5)^4=256`

`=>(3x-5)^4=(4)^4=(-4)^4`

`=>[(3x-5=4),(3x-5=-4):}`

`=>[(3x=9),(3x=1):}`

`=>[(x=3),(x=1/3):}`

Vậy `x=3` hoặc `x=1/3.`

Ta có: \(\left(3x-5\right)^4=256\)

\(\Leftrightarrow\left[{}\begin{matrix}3x-5=4\\3x-5=-4\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}3x=9\\3x=1\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=3\\x=\dfrac{1}{3}\end{matrix}\right.\)

a) 

5.(12-x)-20=30

⇒60-5x-20=30

⇒-5x=30+20-60

⇒-5x=-10

⇒x=2

b)(17x - 25 ) : 8 + 65 = 9²

(17x - 25 ) : 8 + 65 = 81

17x - 25 = 16 x 8 = 128

17x = 128+25=153

x= 153:17 =9

c)

x=23

Giải thích các bước giải:

3x – 10 = 2x + 13

3x-2x=13+10

x=23

d)4(2x+7)-3(3x-2)=24

4.2x+4.7-3.3x+3.2=24

8x+28-9x+6=24

8x-9x=24-28-6=-10

=>(-1)x=-10

        x=-10:(-1)

        x=10

a. \(5\cdot\left(12-x\right)-20=30\Leftrightarrow5\left(12-x\right)=50\)

\(\Leftrightarrow12-x=50:5=10\)

\(\Leftrightarrow x=12-10=2\)

b. \(\left(17x-25\right):8+65=9^2\)

\(\Leftrightarrow\left(17x-25\right):8=81-65=16\)

\(\Leftrightarrow17x-25=16:8=2\)

\(\Leftrightarrow17x=2+25=27\Leftrightarrow x=\frac{27}{17}\)

c. \(3x-10=2x+13\)

\(\Leftrightarrow3x-2x=10+13\)

\(\Leftrightarrow x=23\)

d. \(4\cdot\left(2x+7\right)-3\cdot\left(3x-2\right)=24\)

\(\Leftrightarrow8x+28-9x+6=24\)

\(\Leftrightarrow34-x=24\Leftrightarrow x=10\)

\(15-2\left(3x+1\right)=9^2\cdot4^2\cdot5\)

\(=15-2\left(3x+1\right)=6480\)

\(\Rightarrow2\left(3x+1\right)=15-6480=-6465\)

\(\Rightarrow3x+1=-6465:2=-3232,5\)

\(\Rightarrow3x=-3232,5-1=-3233,5\)

\(\Rightarrow x=-3233,5:3=\frac{-6467}{6}=-1077,833333\)