Bài 1:

\(\frac{4}{3.5}+\frac{4}{5.7}+...+\frac{4}{97.99}\)

\(=2\left(\frac{2}{3.5}+\frac{2}{5.7}+...+\frac{2}{97.99}\right)\)

\(=2\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{97}-\frac{1}{99}\right)\)

\(=2\left(\frac{1}{3}-\frac{1}{99}\right)\)

\(=2.\frac{32}{99}=\frac{64}{99}\)

Bài 2:

a) \(2.4^x-18=110\)

\(\Leftrightarrow2.4^x=128\)

\(\Leftrightarrow4^x=64\)

\(\Leftrightarrow4^x=4^3\Leftrightarrow x=3\)

Vậy x = 3

b) \(\left(\frac{3}{2}x-1\right)^5=1\)

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

\(\Leftrightarrow\frac{3}{2}x=2\)

\(\Leftrightarrow x=\frac{4}{3}\)

Vậy \(x=\frac{4}{3}\)

a) 4/3.5 + 3/5.7 + .... + 4/97.99

= 4( 1/3.5 +1/5.7 + ... + 1/97.99 )

= 4 . 1/2 . 2 ( 1/3.5 +1/5.7 + ... + 1/97.99 )

= 4/2 ( 2/3.5 + 2/5.7 + .... + 2/97.99 )

= 2 ( 5-3/3.5 + 7-5/5.7 + ..... + 99-97/97.99 )

= 2 (5/3.5 - 3/3.5 + 7/5.7 - 5/5.7 + .... + 99/97.99 - 97/97.99 )

= 2 ( 1/3 - 1/5 + 1/5 - 1/7 + ..... + 1/97 - 1/99 )

= 2 ( 1/3 -1/99 )

= 2 (33/99 - 1/99 )

= 2 . 32/99

= 32.2/99

=64/99

b) 2. 4^x  - 18 = 110

    2. 4^x = 110 + 18

    2. 4^x = 128 

    4^x = 128 : 2

    4^x = 64

    4^x = 4³

=> x = 3

Bài 1: Tính nhanh 

A, 13 x 126 + 37 x 126 - 49 x 126

= 126 x ( 13 + 49 - 49 )

= 126 x 1

= 126

B, ( 1 + 2 + 4 + 8+.....+ 512 ) x ( 101 x 102 - 101 x 101 - 50 - 51 )

= ( 1 + 2 + 4 + 8+.....+ 512 ) x ( 101 x ( 102 - 101 - 1))

= ( 1 + 2 + 4 + 8+.....+ 512 ) x ( 101 x 0)

= ( 1 + 2 + 4 + 8+.....+ 512 ) x 0

= 0

Bài 2 

a)  \(x\times1\frac{1}{4}=3\frac{3}{4}\)

\(x\times\frac{5}{4}=\frac{15}{4}\)

\(x=\frac{15}{4}.\frac{4}{5}\)

\(x=3\)

b) \(x-\frac{3}{4}=6\times\frac{3}{8}\)

\(x-\frac{3}{4}=\frac{9}{4}\)

\(x=\frac{9}{4}+\frac{3}{4}\)

\(x=3\)

Những câu còn lại tương tự

=>2/1*3+2/3*5+...+2/(2x-1)(2x+1)=98/99

=>1-1/3+1/3-1/5+...+1/(2x-1)-1/(2x+1)=98/99

=>1-1/(2x+1)=98/99

=>1/(2x+1)=1/99

=>2x+1=99

=>x=49

\(\left(1+\frac{1}{1.3}\right)\left(1+\frac{1}{2.4}\right).....\left(1+\frac{1}{99.101}\right)\)

\(=\frac{2.2}{1.3}\frac{3.3}{2.4}.....\frac{100.100}{99.101}\)

\(=\frac{\left(2.3.4.....100\right).\left(2.3.4.....100\right)}{\left(1.2.3.....99\right).\left(3.4.5.....101\right)}\)

\(=\frac{100.2}{101}=\frac{200}{101}\)

\(\frac{\left(x-3\right)\left(x+5\right)}{\left(x-2\right)^2}< 0\)

\(\Rightarrow\frac{\left(x-3\right)\left(x+5\right)}{\left(x-2\right).\left(x-2\right)}< 0\)

=> ( x - 3 ) . ( x - 5 ) và ( x - 2 ) . ( x - 2 ) trái dấu 

Mà ( x - 2 )² = ( x - 2 ) . ( x - 2 ) ≥ 0 ∀ x

 \(\Rightarrow\hept{\begin{cases}\left(x−3\right).\left(x+5\right)< 0\\\left(x−2\right).\left(x−2\right)>0\end{cases}}\)

\(\Rightarrow\hept{\begin{cases}x< −5;−5< x< 3\\x>2\end{cases}}\)

\(\Rightarrow\hept{\begin{cases}x< −5\\2< x< 3\end{cases}}\)

1.\(\dfrac{11}{8}\)

2.A)739\(\times\) (2+1+3+4)=7390

B)801\(\times\) (67+34-1)=80100