a) `A=a. 1/3 + a. 1/4 - a.1/6 = a. (1/3+1/4 -1/6)=a. 5/12`
Thay `a=-3/5: A=-3/5 . 5/12 =-1/4`
b) `B=b. 5/6+ b. 3/4-b. 1/2=b.(5/6+3/4-1/2)=b. 13/12`
Thay `b=12/13: B=12/13 . 13/12=1`.
a) Ta có: \(A=a\cdot\dfrac{1}{3}+a\cdot\dfrac{1}{4}-a\cdot\dfrac{1}{6}\)
\(=a\left(\dfrac{1}{3}+\dfrac{1}{4}-\dfrac{1}{6}\right)\)
\(=a\cdot\left(\dfrac{4}{12}+\dfrac{3}{12}-\dfrac{2}{12}\right)\)
\(=a\cdot\dfrac{5}{12}\)
\(=\dfrac{-3}{5}\cdot\dfrac{5}{12}=\dfrac{-1}{4}\)
b) Ta có: \(B=b\cdot\dfrac{5}{6}+b\cdot\dfrac{3}{4}-b\cdot\dfrac{1}{2}\)
\(=b\left(\dfrac{5}{6}+\dfrac{3}{4}-\dfrac{1}{2}\right)\)
\(=b\cdot\left(\dfrac{10}{12}+\dfrac{9}{12}-\dfrac{4}{12}\right)\)
\(=b\cdot\dfrac{5}{4}\)
\(=\dfrac{12}{13}\cdot\dfrac{5}{4}=\dfrac{60}{52}=\dfrac{15}{13}\)
a) \(A=a\cdot\dfrac{1}{3}+a\cdot\dfrac{1}{4}-a\cdot\dfrac{1}{6}\\ A=a\cdot\left(\dfrac{1}{3}+\dfrac{1}{4}-\dfrac{1}{6}\right)\\ A=a\cdot\dfrac{-5}{12}\)
Khi \(a=\dfrac{-3}{5}\), ta có:
\(A=\dfrac{-3}{5}\cdot\dfrac{-5}{12}\\ A=\dfrac{1}{4}\)
Vậy khi \(a=\dfrac{-3}{5}\) thì \(A=\dfrac{1}{4}\)
b. \(B=b\cdot\dfrac{5}{6}+b\cdot\dfrac{3}{4}-b\cdot\dfrac{1}{2}\\ B=b\cdot\left(\dfrac{5}{6}+\dfrac{3}{4}-\dfrac{1}{2}\right)\\ B=b\cdot\dfrac{13}{12}\)
Khi \(a=\dfrac{12}{13}\), ta có:
\(B=\dfrac{12}{13}\cdot\dfrac{13}{12}\\ B=1\)
Vậy khi \(a=\dfrac{-3}{5}\) thì B = 1
A= a(⅓+¼+⅙)
Thay a=-⅗ vào bt A ta được
-⅗(8/24+6/24+4/24)=-⅗*7/12=-21/60=7/20
Rối quá nhiều đáp án vậy sao mk bt câu nào đúng, sai chứ ??
