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

Answer 1

a) Vì

)

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=\(\dfrac{62}{15}\)