Question

[Hoàng Thị Huyền Trang]

bài 1 : tìm x biết 

a, ( x - 2 ) : 2 x 3 = 6

b, X : ( hỗn số 3 1/2 x hỗn số 2 2/3 ) = 9/56

c, 1 + 3 + 5 + .....+ ( 2 x X + 1 ) = 625

bài 2 : tìm x biết

a,  ( x - 1/2 ) x 5/3 = 7/4 - 1/2

b, 5 x X + X = 42

c, ( x+1 ) + ( x+ 3 ) + ( x + 5 ) + ....+ ( x + 11 ) = 58

bài 3 tìm x biết

a, X - 1,25 x 4 = 7,5

b, X = ( hỗn số 6 3/5 : 6 - 0 , 125 x 8 + hỗn số 2 2/15 x 0,03 ) x 2/11

c, ( X + 1 ) +(X + 2 ) + ( X + 3 ) + ....+(X + 20 ) = 750

Answer 1

[Trí Tiên亗]

1 

\(\left(x-2\right):2.3=6\)

\(\Leftrightarrow\left(x-2\right):2=2\)

\(\Leftrightarrow\left(x-2\right)=4\)

\(\Leftrightarrow x=4+2=6\)

c) ta có

\(\left[\left(2x+1\right)+1\right]m:2=625\)

\(\Leftrightarrow\left[\left(2x+1\right)+1\right]\left\{\left[\left(2x+1\right)-1\right]:2+1\right\}=1250\)

\(\Leftrightarrow\left(2x+1\right)^2+1-1:2+1=1250\)

\(\Leftrightarrow\left(2x+1\right)^2+1-2+1=1250\)

\(\Leftrightarrow\left(2x+1\right)^2+1-2=1249\)

\(\Leftrightarrow\left(2x+1\right)^2+1=1251\)

\(\Leftrightarrow\left(2x+1\right)^2=1250\)

...

2

\(\left(x-\frac{1}{2}\right).\frac{5}{3}=\frac{7}{4}-\frac{1}{2}\)

\(\Leftrightarrow\left(x-\frac{1}{2}\right).\frac{5}{3}=\frac{5}{4}\)

\(\Leftrightarrow\left(x-\frac{1}{2}\right)=\frac{5}{4}:\frac{5}{3}\)

\(\Leftrightarrow\left(x-\frac{1}{2}\right)=\frac{5}{4}.\frac{3}{5}\)

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

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