Question

Bài 2.Tìm x:

a) 2017-(x-17)=169:13

b) [(25-x).3+21]:2-4=23

c)1+3+5+...+x=1600

Answer 1

Ta có : 1 + 3 + 5 + ..... + x = 1600

=> \(\frac{\text{[(x - 1) : 2 + 1](x + 1)}}{2}=1600\)

\(\Rightarrow\left(\frac{1}{2}x-\frac{1}{2}+1\right)\left(x+1\right)=3200\)

\(\Rightarrow\left(\frac{1}{2}x+\frac{1}{2}\right)\left(x+1\right)=3200\)

\(\Rightarrow\left(x+1\right)^2.\frac{1}{2}=3200\)

\(\Rightarrow\left(x+1\right)^2=6400\)

\(\Rightarrow x+1=80\)

=> x = 79