[Toán 7]Bài tập

D

dinhthimai9x

Bài 46 :
a>3,6x=-2*27--->x=-15
b>-0,52/x=-9,36/16,38<--->-9,36*x=-0,52*16,38--->x=0,91
c>4/1/4*1,61=x*2/7/8---->x=2,38
Bài 44:
a>1,2/3,24=10/27
b>2/1/5:3/4=44/15
c>2/7:0,42=100/147
Bài 45:
3/10=2,1/7 ;28/14=8/4
Bài 43
S=2^2+4^2+6^2+...+20^2=(1*2)^2(2*2)^2+(2*3)^2+...+(2*10)^2=1^2*2^2+2^2*2^2+2^2*3^2+...+2^2*10^2
=2^2*(1^2+2^2+3^2+4^2+..........+10^2=4*385=bạn tự tính
 
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