Question

Tính B=\(\left(\dfrac{7}{19.31}+\dfrac{5}{19.43}+\dfrac{3}{23.43}+\dfrac{11}{23.57}\right)\):\(\left(\dfrac{1}{31}-\dfrac{1}{57}\right)\)

Làm nhanh cho mình nha!!Mai thi rùi

Answer 1

\(B=\left(\dfrac{7}{19\cdot31}+\dfrac{5}{19\cdot43}+\dfrac{3}{23\cdot43}+\dfrac{11}{23\cdot57}\right):\left(\dfrac{1}{31}-\dfrac{1}{57}\right)\)

\(\Rightarrow\dfrac{1}{2}B=\left(\dfrac{7}{38\cdot31}+\dfrac{5}{38\cdot43}+\dfrac{3}{46\cdot43}+\dfrac{11}{46\cdot57}\right):\left(\dfrac{1}{31}-\dfrac{1}{57}\right)\)

\(\Rightarrow\dfrac{1}{2}B=\left(\dfrac{1}{31}-\dfrac{1}{38}+\dfrac{1}{38}-\dfrac{1}{43}+\dfrac{1}{43}-\dfrac{1}{46}+\dfrac{1}{46}-\dfrac{1}{57}\right):\left(\dfrac{1}{31}-\dfrac{1}{57}\right)\)

\(\Rightarrow\dfrac{1}{2}B=\left(\dfrac{1}{31}-\dfrac{1}{57}\right):\left(\dfrac{1}{31}-\dfrac{1}{57}\right)\)

\(\Rightarrow\dfrac{1}{2}B=1\)

\(\Rightarrow B=1:\dfrac{1}{2}=2\)

Answer 2

Đáp án = 2