A bang 1.2+2.3+3,4+….+15.16+16.17+17.18 giups em voi a 15/08/2021 Bởi Athena A bang 1.2+2.3+3,4+….+15.16+16.17+17.18 giups em voi a
A= 1.2+2.3+3,4+….+15.16+16.17+17.18 3.A= 1.2.3 + 2.3.3+….+ 3.17.18 3.A= 1.2 . ( 3- 0] + 2.3 . ( 4- 1] +…+ 17.18. ( 19- 16] 3.A= 1.2.3 + 2.3.4 – 1.2.3 +….+ 17.18.19 3.A= 17. 18. 19 A= 17. 6. 19 A= 1938 Học tốt nhé! Bình luận
Đáp án: $ A=1938$ Giải thích các bước giải: Ta có:$A=1.2+2.3+3.4+…+15.16+16.17+17.18$ $\to 3A=1.2.3+2.3.3+3.4.3+…+15.16.3+16.17.3+17.18.3$ $\to 3A=1.2.(3-0)+2.3.(4-1)+3.4.(5-2)+…+15.16.(17-14)+16.17.(18-15)+17.18.(19-16)$ $\to 3A=-0.1.2+1.2.3-1.2.3+2.3.4-2.3.4+3.4.5+…-14.15.16+15.16.17-15.16.17+16.17.18-16.17.18+17.18.19$ $\to 3A=17.18.19$ $\to A=\dfrac{17.18.19}{3}$ $\to A=1938$ Bình luận
A= 1.2+2.3+3,4+….+15.16+16.17+17.18
3.A= 1.2.3 + 2.3.3+….+ 3.17.18
3.A= 1.2 . ( 3- 0] + 2.3 . ( 4- 1] +…+ 17.18. ( 19- 16]
3.A= 1.2.3 + 2.3.4 – 1.2.3 +….+ 17.18.19
3.A= 17. 18. 19
A= 17. 6. 19
A= 1938
Học tốt nhé!
Đáp án: $ A=1938$
Giải thích các bước giải:
Ta có:
$A=1.2+2.3+3.4+…+15.16+16.17+17.18$
$\to 3A=1.2.3+2.3.3+3.4.3+…+15.16.3+16.17.3+17.18.3$
$\to 3A=1.2.(3-0)+2.3.(4-1)+3.4.(5-2)+…+15.16.(17-14)+16.17.(18-15)+17.18.(19-16)$
$\to 3A=-0.1.2+1.2.3-1.2.3+2.3.4-2.3.4+3.4.5+…-14.15.16+15.16.17-15.16.17+16.17.18-16.17.18+17.18.19$
$\to 3A=17.18.19$
$\to A=\dfrac{17.18.19}{3}$
$\to A=1938$