`2/15 + 7/5 = 2/15 + 21/15 = 23/15`

`3/5 xx 8/11 = 24/55`

`4- 13/4 = 16/4 - 13/4 = 3/4`

`2: 1/3 = 2xx3=6`

nhân -4 thì ra 41/16 chứ :V

\(\dfrac{25}{64}-\dfrac{9}{24}=\dfrac{1}{4}\) mà

quá thời gian ko sửa đc :V

tui ra `41/16` mà

uk nhỉ :V

\(\dfrac{18}{-36}-\dfrac{54}{81}-\dfrac{60}{90}+\dfrac{-2}{5}\\ =\dfrac{-1}{2}-\dfrac{2}{3}-\dfrac{2}{3}+\dfrac{-2}{5}\\ =\dfrac{-15}{30}-\dfrac{20}{30}-\dfrac{20}{30}+\dfrac{-12}{30}\\ =\dfrac{-15-20-20+\left(-12\right)}{30}\\ =\dfrac{-67}{30}\)

sai r

\(P=-4x^2-5x+1\\ =-4\left(x^2+\dfrac{5}{4}x-\dfrac{1}{4}\right)\\ =-4\left(x^2+2.\dfrac{5}{8}x+\dfrac{25}{64}-\dfrac{41}{64}\right)\\ =-4\left[\left(x+\dfrac{5}{8}\right)^2-\dfrac{41}{64}\right]\\ =-4\left(x+\dfrac{5}{8}\right)^2+\dfrac{41}{16}\le\dfrac{41}{16}\)

Dấu "=" xảy ra `<=>x= -5/8`

Vậy `P_(max)= 41/16 <=> x= -5/8`