Question

Bài 9: Tìm x, biết: a) (x-3)^2=1; b) ( x - 1/ 7 )^2 =0 ; c) ( 2x +3)^3= -27; d) ( 2+1/2)^2 =1/4 .x; e) -(5+35.x)^2=36

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Answer 1

a) \(\left(x-3\right)^2=1\)

\(\Leftrightarrow x-3=1\)

\(\Leftrightarrow x=4\)

b) \(\left(x-\frac{1}{7}\right)^2=0\)

\(\Leftrightarrow x-\frac{1}{7}=0\)

\(\Leftrightarrow x=\frac{1}{7}\)

c) \(\left(2x+3\right)^3=-27=\left(-3\right)^3\)

\(\Leftrightarrow2x+3=-3\)

\(\Leftrightarrow2x=-6\)

\(\Leftrightarrow x=-3\)

d) \(\left(2+\frac{1}{2}\right)^2=\frac{1}{4}.x\)

\(\Leftrightarrow\frac{25}{4}=\frac{1}{4}.x\)

\(\Leftrightarrow x=\frac{25}{4}:\frac{1}{4}\)

\(\Leftrightarrow x=25\)

e) \(-\left(5+35.x\right)^2=36=6^2\)

\(\Leftrightarrow-\left(5+35.x\right)=6\)

\(\Leftrightarrow5+35.x=-6\)

\(\Leftrightarrow35.x=-6-5=-11\)

\(\Leftrightarrow x=-\frac{11}{35}\)

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