a)  x = 1 5 + 2 11 ⇔ x = 1.11 + 2.5 55 = 21 55

b)  x 5 = 5 6 + − 19 30 ⇔ x 5 = 5.5 + ( − 19 ) 30 = 6 30 = 1 6 ⇔ x = 5 6

9999 < 10 000

653 211 = 653 211

99 999 < 100 000

43 256 < 432 510

726 585 > 557 652

845 713 < 854 713

9999 < 10 000

653 211 = 653 211

99 999 < 100 000

43 256 < 432 510

726 585 > 557 652

845 713 < 854 713

9999<10000

653211=653211

99999<100000

43256<4325`10

726585>557652

845713<854713

 253 - (-76 + 253) + 99 =175

68 - (199 + 68) - (-150) = -49

211 - (107 + 211) - 23 = -130

-(-345 + 56 - 267) + (453 - 124 - 843) =42

-25 - (34 - 256 + 67) - (-2) + (-10 - 65) =57.

\(\frac{217-x}{207}+\frac{215-x}{209}+\frac{213-x}{211}+\frac{211-x}{213}+4=0\)

\(\Leftrightarrow\)\(\left(\frac{217-x}{207}+1\right)+\left(\frac{215-x}{209}+1\right)+\left(\frac{213-x}{211}+1\right)+\left(\frac{211-x}{213}+1\right)=0\)

\(\Leftrightarrow\)\(\frac{424-x}{207}+\frac{424-x}{209}+\frac{424-x}{211}+\frac{424-x}{213}=0\)

\(\Leftrightarrow\)\(\left(424-x\right)\left(\frac{1}{207}+\frac{1}{209}+\frac{1}{211}+\frac{1}{213}\right)=0\)

\(\Leftrightarrow\)\(424-x=0\)   (do 1/207 + 1/209 + 1/211 + 1/213 # 0)

\(\Leftrightarrow\)\(x=424\)

Vậy...

a ) x = 21 55 ; b ) x = − 11 26 ; c ) x = 11 18 ; d ) x = 1

d ) x = − 1 ; e ) x = 11 7 ; f ) x = 20

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