;((

`3,4m^2=3,4xx100=340dm^2`

`S=1+2+2^2+2^3+..+2^2017`

`2S=2+2^2+2^3+2^4+...+2^2018`

`2S-S=(2+2^2+2^3+2^4+...+2^2018)-(1+2+2^2+2^3+...+2^2017)`

`S=2^2018-1`

`8^7:8^4:8` (đề như thế này phải không ạ?)

`=8^(7-4-1)`

`=8^2`

`=64`

`2^x-26=6`

`2^x=6+26`

`2^x=32`

`2^x=2^5`

`=>x=5`

\(cos\alpha=\dfrac{3}{5}=>cos^2\alpha=\dfrac{9}{25}\)

có \(sin^2\alpha+cos^2\alpha=1< =>sin^2\alpha+\dfrac{9}{25}=1=>sin\alpha=\dfrac{4}{5}\left(sin\alpha>0\right)\)

\(tan\alpha=\dfrac{sin\alpha}{cos\alpha}=\dfrac{\dfrac{4}{5}}{\dfrac{3}{5}}=\dfrac{4}{3}\)

\(cot\alpha\cdot tan\alpha=1=>cot\alpha\cdot\dfrac{4}{3}=1=>cot\alpha=\dfrac{3}{4}\)

`(3x-1)^2=25`

`=>3x-1=5` hoặc `3x-1=-5`

`=>x=2` hoặc `x=-4/3`