Đáp án:
Bài 16:
`* (-43)/51 . (-19)/80 = 43/51 . 19/80 > 0`
`* (-7)/13 . (-4)/65 . (-8)/31 = - (7/13 . 4/65 . 8/31) < 0`
`* (-5)/10 . (-4)/10 . (-3)/10 ............. 3/10 . 4/10 . 5/10`
`=(-5)/10 . (-4)/10 . (-3)/10 ..... 0 . 1/10 . 2/10 . 3/10 . 4/10 . 5/10 = 0`
Hay $P_{1}$ >$P_{3}$ >$P_{2}$
Bài 17:
a, `(1/7x - 2/7)(-1/5x + 3/5)(1/3x + 4/3)=0`
⇒\(\left[ \begin{array}{l}\frac{1}{7}x - \frac{2}{7} = 0 \\\frac{-1}{5}x + \frac{3}{5} = 0 \\\frac{1}{3}x + \frac{4}{3} =0\end{array} \right.\)
⇒\(\left[ \begin{array}{l}\frac{1}{7}x = \frac{2}{7} \\\frac{-1}{5}x =- \frac{3}{5}\\\frac{1}{3}x =- \frac{4}{3} \end{array} \right.\)
⇒\(\left[ \begin{array}{l}x=2\\x=-3\\ x = -4\end{array} \right.\)
Vậy `x ∈{ 2 ; -3 ; -4}`
b, `1/6 x + 1/10 x - 4/15 x + 1 =0`
`x(1/6 + 1/10 - 4/15) = 0 - 1`
`x(5/30 + 3/30 - 8/30) = -1`
`x0 = -1`
`text{ ⇒ Vô lí}`
