Đáp án:
a, `-5/3 + 1/2 : 3/4`
` = -5/3 + 2/3`
` = -3/3 = -1`
b, `-3/7 - 4/9 + 10/7 - 23/9 + 2/3`
` = (10/7 - 3/7) - (23/9 + 4/9) + 2/3`
` = 1 - 3 + 2/3`
` = -2 + 2/3 = -4/3`
c, `9/4 : ( -3,5) + 9/4 : 2 2/7`
` = 9/4 . -2/7 + 9/4 . 7/16`
` = 9/4 . (-2/7 + 7/16)`
` = 9/4 . 17/112`
` = 153/448`
Tìm x:
a, `60% x - x + 1/3 = 2`
` 3/5 x - x = 2 - 1/3`
` -2/5 x = 5/3`
` x = 5/3 : -2/5`
` x = -25/6`
b, `x + 1/7 = 1/2`
` x = 1/2 - 1/7`
` x = 5/14`
c, ` (4x^2 - 25)(x + 3) = 0`
⇒\(\left[ \begin{array}{l}4x^2 - 25 = 0\\x +3 = 0\end{array} \right.\)
⇒\(\left[ \begin{array}{l}x^2 = \frac{25}{4}\\x = 0 - 3\end{array} \right.\)
⇒\(\left[ \begin{array}{l}x= ±\frac{5}{2}\\x = - 3\end{array} \right.\)
Vậy `x \in { 5/2 ; -5/2 ; -3}`
