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A= 1/5.9+1/9.13+1/13.17+1/17.21+1/21.25
4A= 4/5.9+4/9.13+4/13.17+4/17.21+4/21.25
4A= (1/5-1/9)+(1/9-1/13)+(1/13-1/17)+(1/17-1/21)+(1/21-1/25)
4A= 1/5- 1/25
4A= 4/25
A= 4/25 :4
A= 1/25
bài này nâng cao lớp 6 mk giải rồi bạn nhờ ai giảng hộ nha nếu bn 5 lên 6
B=1/4.(4/1.5+4/5.9+......+4/25.29)
B=1/4.(1-1/5+1/5-1/9+.....+1/25-1/29)
B=1/4.(1-1/29)
B=1/4.28/29
B=7/29
\(B=\frac{1}{1.5}+\frac{1}{5.9}+\frac{1}{9.13}+\frac{1}{13.17}+\frac{1}{17.21}+\frac{1}{21.25}+\frac{1}{25.29}\)
\(\Rightarrow4B=\frac{4}{1.5}+\frac{4}{5.9}+\frac{4}{9.13}+\frac{4}{13.17}+\frac{4}{17.21}+\frac{4}{21.25}+\frac{4}{25.29}\)
\(\Rightarrow4B=1-\frac{1}{5}+\frac{1}{5}-\frac{1}{9}+\frac{1}{9}-\frac{1}{13}+\frac{1}{13}-\frac{1}{17}+\frac{1}{17}-\frac{1}{21}+\frac{1}{21}-\frac{1}{25}+\frac{1}{25}-\frac{1}{29}\)
\(\Rightarrow4B=1-\frac{1}{29}\)
\(\Rightarrow4B=\frac{29}{29}-\frac{1}{29}=\frac{28}{29}\)
\(\Rightarrow B=\frac{28}{29}:4=\frac{28}{29}.\frac{1}{4}=\frac{7}{29}\)
Vậy ....
\(\frac{4,8\left(1994+3996+4010\right)}{\left(\frac{99-3}{4}+1\right)\left(\frac{99+3}{2}\right)-11.25}=\frac{48000}{25.51-11.25}=\frac{48000}{1000}=48\)
y+y:0.5+y:0.25=y:0.125=125
=y+yx2+yx4+yx8=125
=yx15=125
y=125:15
y=25/3
4,5 x y - y x 125% + y : 5/7 + 1/4 x y = 17,1
4,5 x y - y x 8 + y .7/5 + 1/4 x y =17,1
y x (4,5-8+7/5+1/4)=17,1
y x (-1,85)=17,1
y=17,1 : (-1,85)
y=.............(tự tính )
\(4,5\times y-y\times125\%+y:\frac{5}{7}+\frac{1}{4}\times y=17,15\)
=> \(4,5\times y-y\times1,25+y\times1,4+0,25\times y=17,15\)
=> \(y\times\left(4,5-1,25+1,4+0,25\right)=17,15\)
=> \(y\times4,9=17,15\)
=> \(y=17,15:4,9\)
=> \(y=3,5\)
Study well ! >_<
Đáp án Y= 0,08.
\(21,25-125y=11,25\)
\(\Rightarrow125y=10\left(\text{cùng bớt đi 11 , 25}\right)\)
\(\Rightarrow y=\frac{2}{25}\)