Câu hỏi của Hoàng Thúy An

Question

cho A = 3a - 4ab + 5b . tinh gia tri cua A khi

a, $\left|a\right|=\dfrac{3}{4},b=\dfrac{-5}{6}$

b,$a=\dfrac{-2}{3},b=\dfrac{4}{5}$

giup minh nhe minh dang can gap

Khải Vũ · Accepted Answer

a) Vì |a|=$\dfrac{3}{4}$=>a=$\dfrac{3}{4}$.Thay vào ta sẽ có:

A=3.$\dfrac{3}{4}$-4.$\dfrac{3}{4}$.($\dfrac{-5}{6}$)+5.($\dfrac{-5}{6}$)

A=$\dfrac{9}{4}-\left(\dfrac{-5}{2}\right)+\left(\dfrac{-25}{6}\right)$

A=$\dfrac{19}{4}$-$\dfrac{25}{6}$

A=$\dfrac{14}{24}$=$\dfrac{7}{12}$

b, Thay vào, ta sẽ có:

A=3.$\left(\dfrac{-2}{3}\right)-4.\left(\dfrac{-2}{3}\right).\dfrac{4}{5}+5.\dfrac{4}{5}$

A=-2-$\left(\dfrac{-32}{15}\right)$+4

A=$\dfrac{2}{15}$+4

A=$\dfrac{62}{15}$Câu trả lời: a) Vì |a|=$\dfrac{3}{4}$=>a=$\dfrac{3}{4}$.Thay vào ta sẽ có: