Question

CÁC BẠN GIẢI THÍCH GIÙM MÌNH CÁCH LÀM BÀI NÀY VỚI

A=1.2+2.3+3.4+4.5+5.6+6.7+7.8+8.9+9.10

Answer 1

3A=1.2.3+2.3.(4-1)+3.4.(5-2)+4.5.(6-3)+5.6.(7-4)+6.7.(8-5)+7.8.(9-6)+8.9.(10-7)+9.10.(11-8)

=1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+4.5.6-3.4.5+5.6.7-4.5.6+6.7.8-5.6.7+7.8.9-6.7.8+8.9.10-7.8.9+9.10.11-8.9.10

=9.10.11

=> A=9.10.11:3

=3.10.11

=330

Answer 2

3A= 3.(1.2 + 2.3 + 3.4 + 4.5 + 5.6 + 6.7 + 7.8 + 8.9 + 9.10)
= 1.2.(3 - 0) + 2.3.(4 - 1) + 3.4.(5 - 2) + 4.5.(6 - 3) + 5.6.(7 - 4) + 6.7.(8 - 5) + 7.8.(9 - 6) + 8.9.(10 - 7) + 9.10.(11 - 8)
= 1.2.3 - 1.2.3 + 2.3.4 - 2.3.4 + 3.4.5 - … + 8.9.10 - 8.9.10 + 9.10.11
= 9.10.11 = 990.
A= 990/3 = 330

Answer 3

\(A=1.2+2.3+3.4+4.5+5.6+6.7+7.8+8.9+9.10\)

\(A=2.\left(1+3\right)+4.\left(3+5\right)+6.\left(5+7\right)+8.\left(7+9\right)+9.10\)

\(A=8+32+72+128+90\)

\(A=330\)