Toán Lớp 7: tìm x thỏa mãn: a)(2x-1)(2x-5) bé hơn hoặc bằng 0 b)(2x+1)(2x+7) lớn hơn hoặc bằng 0 giúp mik nha

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Toán Lớp 7:  tìm x thỏa mãn: a)(2x-1)(2x-5) bé hơn hoặc bằng 0                              b)(2x+1)(2x+7) lớn hơn hoặc bằng 0 giúp mik nha

hienchaudiem · Answer

Giải đáp:   $a)   dfrac{1}{2}  le  x  le   dfrac{5}{2}   b)  left[ begin{array}{l} x ge  dfrac{-1}{2}   x  le  dfrac{-7}{2} end{array}  right.$   Lời giải và giải thích chi tiết:   $a)(2x-1)(2x-5)  le 0     Leftrightarrow   left[ begin{array}{l}   left { begin{array}{l} 2x-1  ge 0   2x-5  le 0 end{array}  right.    left { begin{array}{l} 2x-1  le 0   2x-5  ge 0 end{array}  right. end{array}  right.    Leftrightarrow   left[ begin{array}{l}   left { begin{array}{l} 2x ge 1   2x  le 5 end{array}  right.    left { begin{array}{l} 2x  le 1   2x  ge 5 end{array}  right. end{array}  right.   Leftrightarrow   left[ begin{array}{l}   left { begin{array}{l} x ge  dfrac{1}{2}   x  le  dfrac{5}{2} end{array}  right.    left { begin{array}{l} x  le  dfrac{1}{2}   x  ge  dfrac{5}{2} end{array}  right.( text{V&ocirc; l&iacute;}) end{array}  right.    Leftrightarrow    dfrac{1}{2}  le  x  le   dfrac{5}{2}   b)(2x+1)(2x+7)  ge 0     Leftrightarrow  left[ begin{array}{l}  left { begin{array}{l} 2x+1  ge 0   2x+7  ge 0 end{array}  right.    left { begin{array}{l} 2x+1  le 0   2x+7  le 0 end{array}  right. end{array}  right.    Leftrightarrow  left[ begin{array}{l}  left { begin{array}{l} 2x ge -1   2x  ge -7 end{array}  right.    left { begin{array}{l} 2x  le -1   2x  le -7 end{array}  right. end{array}  right.    Leftrightarrow  left[ begin{array}{l}  left { begin{array}{l} x ge  dfrac{-1}{2}   x  ge  dfrac{-7}{2} end{array}  right.    left { begin{array}{l} x  le  dfrac{-1}{2}   x  le  dfrac{-7}{2} end{array}  right. end{array}  right.    Leftrightarrow  left[ begin{array}{l} x ge  dfrac{-1}{2}   x  le  dfrac{-7}{2} end{array}  right.$