a. \(\frac{7}{8}< \frac{x}{35}< \frac{15}{7}\)
\(\Rightarrow\frac{245}{280}< \frac{8x}{280}< \frac{600}{280}\)
\(\Rightarrow245< 8x< 600\)
\(\Rightarrow30< x< 75\)
\(\Rightarrow x\in\left\{31;32;33;...;72;73;74\right\}\)
b. \(\frac{21}{3}< \frac{x}{7}\le\frac{24}{2}\)
\(\Rightarrow\frac{294}{42}< \frac{6x}{42}\le\frac{504}{42}\)
\(\Rightarrow294< 6x\le504\)
\(\Rightarrow49< x\le84\)
\(\Rightarrow x\in\left\{50;51;52;...;82;83;84\right\}\)
Giải
Có: \(\frac{7}{8}< \frac{x}{35}< \frac{15}{7}\)
=>\(\frac{245}{280}< \frac{x}{280}< \frac{525}{280}\)
=>\(\frac{245}{280}< 1< ....< \frac{525}{280}\)
=>\(x\in\left\{8;9;...;14\right\}\)
b, \(\frac{21}{3}< \frac{x}{7}\le\frac{24}{2}\)
=>\(7< \frac{x}{7}\le12\)
=>\(\frac{49}{7}< \frac{x}{7}\le\frac{12}{7}\)
=>\(\frac{x}{7}=\left\{\frac{12}{7};\frac{14}{7};\frac{21}{7};\frac{28}{7};\frac{35}{7};\frac{42}{7}\right\}\)
=>\(x\in\left\{12;14;21;28;35;42\right\}\)
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