Question

bài 1:tìm x

a)25<2 ngũ x<3125 b)(x+1)+(x+2)+(x+3)+....+(x+100)=7450

c)1+2+3+...+x=78 d)12x+13x=2000

e)6x+4x=2010

Answer 1

Ta có:

a)\(25< 2^x< 3125\)

\(\Rightarrow2^4< 2^x< 2^{12}\)

\(\Rightarrow4< x< 12\)

b)\(\left(x+1\right)+\left(x+2\right)+...+\left(x+100\right)=7450\)

\(\Rightarrow100x+5050=7450\Rightarrow10x=2400\Rightarrow x=240\)

c)\(1+2+3+..+x=\frac{x\left(x+1\right)}{2}=78.\)

\(\Rightarrow x\left(x+1\right)=156\)\(\Rightarrow x=12\)

d)\(12x+13x=25x=2000\Rightarrow x=80\)

e)\(6x+4x=10x=2010\Rightarrow x=201\)