Question

Rút gọn bằng cách thay số bằng chữ 1. A = 4 7/1000 . 1/999 - 1 1/500 . 4/999 + 1001/999.1000 2. B = 1/4587 . 7 1/3897 - 3 4586/4587 . 2/3897 - 7/4587 - 3/4587.3897

Answer 1

1: \(A=4\dfrac{7}{1000}\cdot\dfrac{1}{999}-1\dfrac{1}{500}\cdot\dfrac{4}{999}+\dfrac{1001}{999\cdot1000}\)

Đặt 1/1000=a; 1/999=b

\(A=\left(4+7a\right)\cdot b-\left(1+2a\right)\cdot4b+b\cdot\dfrac{1001}{1000}\)

\(=4b+7ab-4b-8ab+b\cdot\left(1+a\right)\)

=-ab+b+b+ba=2b=2/999

2: Đặt 1/4587=a;1/3897=b

\(B=a\cdot\left(7+b\right)-\left(3+1-a\right)\cdot2b-7a-3ab\)

=7a+ab-8a+2ab-7a-3ab

=-8a=-8/4587