Question

[Trần Bảo Hân]

Giải giúp em bài này em cần ngày mai ạ

4. Tính nhanh:

a, \(A=\frac{27⨉45+27⨉55}{2+4+6+8+...+18}\)

b, \(B=\frac{28⨉108-52⨉12}{32-28+24-20+16-12+8-4}\)

Em cảm ơn trc ạ

Answer 1

[Nguyễn Đăng Nhân]

a) \(A=\frac{27\text{x}45+27\text{x}25}{2+4+6+8+...+18}=\frac{27\left(45+25\right)}{\left(18+2\right)\text{x}\left(\frac{18-2}{2}+1\right)}\)

\(A=\frac{27\text{x}70}{20\text{x}9}=\frac{3\text{x}9\text{x}10\text{x}7}{10\text{x}2\text{x}9}\)

\(A=\frac{21}{2}\)

b) \(B=\frac{28\text{x}108-52\text{x}12}{32-28+24-20+16-12+8-4}\)

\(B=\frac{28\text{x}12\text{x}9\text{​​}\text{​​}-52\text{x}12}{\left(32-28\right)+\left(24-20\right)+\left(16-12\right)+\left(8-4\right)}\)

\(B=\frac{12\left(28\text{x}9-52\right)}{4+4+4+4}=\frac{12\text{x}200}{4\text{x}4}\)

\(B=\frac{4\text{x}3\text{x}4\text{x}50}{4\text{x}4}=150\)

Answer 2

[Trần Bảo Hân]

cám ơn bn