15x15=?
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\(8-\dfrac{1}{15}\)x\(\dfrac{15}{3}\)
\(=8-\)\(\dfrac{15}{45}\)
\(=8-\dfrac{1}{3}\)
\(=\dfrac{24}{3}-\dfrac{1}{3}\)
\(=\dfrac{23}{3}\)
chúc bạn học tốt:>
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
= 1.1! + (3 - 1).2! + (4 - 1).3! + ...+ (16 - 1).15!
= 1! + 3.2! - 2! + 4.3! - 3! + ...+16.15! - 15!
= 1! + 3! - 2! + 4! - 3! + ...+16! - 15!
= 1! + (3! + 4! + ...+ 16!) - (2! + 3! + ...+ 15!)
= 1 + 16! - 2! = ....
Ta có: 1x1!+2x2!+......+15x15!
= 1.1! + (3 - 1).2! + (4 - 1).3! + ...+ (16 - 1).15!
= 1! + 3.2! - 2! + 4.3! - 3! + ...+16.15! - 15!
= 1! + 3! - 2! + 4! - 3! + ...+16! - 15!
= 1! + (3! + 4! + ...+ 16!) - (2! + 3! + ...+ 15!)
= 1 + 16! - 2!
Vậy ...............
hok tốt
![](https://rs.olm.vn/images/avt/0.png?1311)
71x45+15x15+9x100+180
=71x45+5x3x15+9x5x20+45x4
=45x(71+5+20+4)
=45x100=4500
71 x 45 + 15 x 15 + 9 x 100 + 180
= 71 x 45 + 5 x 3 x 15 + 9 x 5 x 20 + 45 x 4
= 45 x ( 71 + 5 + 20 + 4 )
= 45 x 100
= 4500
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\(A=\dfrac{1}{15}\times\dfrac{15}{13}\times\dfrac{13}{9}\times9\)
\(A=\dfrac{1}{15}\times\dfrac{15}{13}\times\dfrac{13}{9}\times\dfrac{9}{1}\)
\(A=\dfrac{1}{1}\)
\(A=1\)
(Sử dụng phương pháp triệt tiêu(rút gọn)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
15 x 15 =225
15x15=225