Tính bằng cách hợp lí nhất : \(\frac{2}{7}\times5\frac{1}{4}-\frac{2}{7}\times3\frac{1}{4}\)
Những câu hỏi liên quan
Tính tổng sau bằng cách hợp lí:
\(A=\frac{1}{1\times2\times3}+\frac{1}{2\times3\times4}+\frac{1}{3\times4\times5}+...+\frac{1}{38\times39\times40}\)
Nhanh và đúng nhất mk tick cho 2 bn nha!!!!!>.<
Suy ra 2A=2/1x2x3+2/2x3x4+2/3x4x5+......+2/38x39x40
2A=3-1/1x2x3+4-2/2x3x4+5-3/3x4x5+........+40-38/38x39x40
2A=1/1x2-1/2x3+1/2x3-1/3x4+1/4x5-1/5x6+........+1/38x39-1/39x40
2A=1/2-1/1560
2A=780/1560-1/1560
2A=779/1560
A=779/1560:2
A=779/1560x1/2
A=779/3120
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\(A=\frac{1}{1.2.3}+\frac{1}{2.3.4}+\frac{1}{3.4.5}+.......+\frac{1}{38.39.40}\)
\(2A=\frac{2}{1.2.3}+\frac{2}{2.3.4}+\frac{2}{3.4.5}+.........+\frac{2}{38.39.40}\)
\(2A=\frac{3-1}{1.2.3}+\frac{4-2}{2.3.4}+\frac{5-3}{3.4.5}+....+\frac{40-38}{38.39.40}\)
\(2A=\frac{3}{1.2.3}-\frac{1}{1.2.3}+\frac{4}{2.3.4}-\frac{2}{2.3.4}+\frac{5}{3.4.5}-\frac{3}{3.4.5}+.......+\frac{40}{38.39.40}-\frac{38}{38.39.40}\)
\(2A=\frac{1}{1.2}-\frac{1}{2.3}+\frac{1}{2.3}-\frac{1}{3.4}+\frac{1}{3.4}-\frac{1}{4.5}+.......+\frac{1}{38.39}-\frac{1}{39.40}\)
\(2A=\frac{1}{1.2}-\frac{1}{39.40}\)
\(2A=\frac{1}{2}-\frac{1}{1560}\)
\(2A=\frac{779}{1560}\)
\(A=\frac{779}{1560}:2\)
\(A=\frac{779}{3120}\)
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tính :\(\frac{1}{1\times2\times3}+\frac{1}{2\times3\times4}+\frac{1}{3\times4\times5}+\frac{1}{4\times5\times6}+\frac{1}{5\times6\times7}+\frac{1}{6\times7\times8}+\frac{1}{7\times8\times9}+\frac{1}{8\times9\times10}\)
\(\frac{1}{1.2.3}+\frac{1}{2.3.4}+...+\frac{1}{8.9.10}=\frac{1}{2}.\left(\frac{1}{1.2}-\frac{1}{2.3}\right)+\frac{1}{2}.\left(\frac{1}{2.3}-\frac{1}{3.4}\right)+...+\frac{1}{2}.\left(\frac{1}{8.9}-\frac{1}{9.10}\right)\)
\(=\frac{1}{2}.\left(\frac{1}{1.2}-\frac{1}{2.3}+\frac{1}{2.3}-\frac{1}{3.4}+...+\frac{1}{8.9}-\frac{1}{9.10}\right)\)
\(\frac{1}{2}.\left(\frac{1}{1.2}-\frac{1}{9.10}\right)=\frac{1}{2}.\frac{22}{45}=\frac{11}{45}\)
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Hỹ tính tổng sau bằng cách hợp lý
\(C=\frac{1}{1\times2\times3\times4}+\frac{1}{2\times3\times4\times5}+...+\frac{1}{27\times28\times29\times30}\)
\(3C=\frac{3}{1.2.3.4}+\frac{3}{2.3.4.5}+...+\frac{3}{27.28.29.30}\)
\(3C=\frac{4-1}{1.2.3.4}+\frac{5-2}{2.3.4.5}+...+\frac{30-27}{27.28.29.30}\)
\(3C=\frac{1}{1.2.3}-\frac{1}{2.3.4}+\frac{1}{2.3.4}-\frac{1}{3.4.5}+...+\frac{1}{27.28.29}+\frac{1}{28.29.30}\)
\(3C=\frac{1}{1.2.3}-\frac{1}{28.29.30}\Rightarrow C=\left(\frac{1}{1.2.3}-\frac{1}{28.29.30}\right):3\)
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a.\(\frac{7^3\times5^8}{49\times25^4}\)
b.\(\frac{3^9\times25\times5^3}{15\times625\times3^8}\)
c.\(\frac{2^{50}\times3^{61}+2^{90}\times3^{16}}{2^{51}\times3^{61}+2^{91}\times3^{16}}\)
d.\((\frac{2}{5}-\frac{1}{2})^2+(\frac{1}{2}+\frac{3}{5})^2\)
a) \(\frac{7^3.5^8}{49.25^4}=\frac{7^3.5^8}{7^2.5^8}=7\)
b) \(\frac{3^9.25.5^3}{15.625.3^8}=\frac{3^9.5^2.5^3}{3.5.5^4.3^8}=\frac{3^9.5^5}{3^9.5^5}=1\)
c) \(\frac{2^{50}.3^{61}+2^{90}.3^{16}}{2^{51}.3^{61}+2^{91}.3^{16}}=\frac{2^{50}.3^{16}\left(3^{45}+2^{40}\right)}{2^{51}.3^{16}\left(3^{45}+2^{40}\right)}=\frac{1}{2}\)
d) \(\left(\frac{2}{5}-\frac{1}{2}\right)^2+\left(\frac{1}{2}+\frac{3}{5}\right)^2\)
\(=\left(\frac{-1}{10}\right)^2+\left(\frac{11}{10}\right)^2\)
\(=\frac{1}{100}+\frac{121}{100}=\frac{122}{100}=\frac{61}{50}\)
a) \(\frac{7^3.5^8}{49.25^4}=\frac{7^3.5^8}{7^2.\left(5^2\right)^4}=\frac{7^3.5^8}{7^2.5^8}=7\)
b) \(\frac{3^9.25.5^3}{15.625.3^8}=\frac{3^9.5^2.5^3}{5.3.5^4.3^8}=\frac{3^9.5^5}{5^5.3^9}=1\)
c) \(\frac{2^{50}.3^{61}+2^{90}.3^{16}}{2^{51}.3^{61}+2^{91}.3^{16}}=\frac{2^{50}.3^{16}\left(3^{45}+2^{40}\right)}{2^{51}.3^{16}\left(3^{45}+2^{40}\right)}=\frac{1}{2}\)
d) \(\left(\frac{2}{5}-\frac{1}{2}\right)^2+\left(\frac{1}{2}+\frac{3}{5}\right)^2=\left(-\frac{1}{10}\right)^2+\left(\frac{11}{10}\right)^2=\frac{1}{100}+\frac{121}{100}=\frac{122}{100}=1,22\)
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frac{left(-7right)^n}{left(-7right)^{n-1}}(nge1) Tính GTBT Bài 2 Tính GTBT theo cách hợp lí nếu có thểc) frac{5^3times3^3}{5^3times0,5+125times2,5}d)frac{5times7^1+7^3times25}{7^5125-7^3times50}e)frac{8^5timesleft(-5right)^8+left(-2right)^5times10^9}{2^{16}times5^7+20^8}h)frac{left(-0,25right)^{-5}times9^4timesleft(-2right)^{-3}-2^{-2}times6^3}{2^9times3^6+6^6times40}Bài 3 Chứng tỏ rằnga)
Đọc tiếp
\(\frac{\left(-7\right)^n}{\left(-7\right)^{n-1}}\)(n\(\ge1\)) Tính GTBT
Bài 2 Tính GTBT theo cách hợp lí nếu có thể
c) \(\frac{5^3\times3^3}{5^3\times0,5+125\times2,5}\)d)\(\frac{5\times7^1+7^3\times25}{7^5125-7^3\times50}\)e)\(\frac{8^5\times\left(-5\right)^8+\left(-2\right)^5\times10^9}{2^{16}\times5^7+20^8}\)
h)\(\frac{\left(-0,25\right)^{-5}\times9^4\times\left(-2\right)^{-3}-2^{-2}\times6^3}{2^9\times3^6+6^6\times40}\)
Bài 3 Chứng tỏ rằng
a)
Tính 1 cách hợp lí nhất :
\(\frac{-2}{5}.\frac{4}{7}+\frac{-3}{5}.\frac{2}{7}+\frac{-3}{5}\)
\(\frac{-3}{5}.\frac{4}{7}+\frac{-3}{5}.\frac{2}{7}+\frac{-3}{5}\)
\(=\frac{-3}{5}.\frac{4}{7}+\frac{-3}{5}.\frac{2}{7}+\frac{-3}{5}.\frac{1}{7}\)
\(=\frac{-3}{5}\left(\frac{4}{7}+\frac{2}{7}+\frac{1}{7}\right)\)
\(=\frac{-3}{5}.1\)
\(=\frac{-3}{5}\)
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\(-\frac{2}{5}x\frac{1}{7}+-\frac{3}{5}x\frac{2}{7}+-\frac{3}{5}=-\frac{2}{5}x\frac{1}{7}+-\frac{3}{5}\left(\frac{2}{7}+1\right)=-\frac{2}{5}x\frac{1}{7}+-\frac{3}{5}x\frac{9}{7}.\)
\(-\frac{2}{35}-\frac{27}{35}=-\frac{29}{35}\)
tôi tính nhẩm vậy ko biết có đứng ko
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\(\frac{1}{2\times3}+\frac{1}{3\times4}+\frac{1}{4\times5}+\frac{1}{5\times6}+\frac{1}{6\times7}+\frac{1}{7\times8}+\frac{1}{8\times9}+\frac{1}{9\times10}\)
1/2.3+1/3.4+1/4.5+1/5.6+1/6.7+1/7.8+1/8.9+1/9.10
=1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6+1/7-1/7+1/8-1/8+1/9+1/9-1/10
=1/2-1/10
=5/10-1/10
=4/10=2/5
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\(\frac{1}{2x3}+\frac{1}{3x4}+\frac{1}{4x5}+\frac{1}{5x6}+\frac{1}{6x7}+\frac{1}{8x9}+\frac{1}{9x10}\)
\(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}\)
\(\frac{1}{2}-\frac{1}{10}\)
\(\frac{2}{5}\)
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= 1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10
= 1/2-0-0-0-0-0-0-0-0-1/10
=1/2 - 1/10
=2/5
tớ trước nhé
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1.Tính giá trị tuyệt đối:(hẹp me)
a)\(\frac{72^3\times54^2}{108^4}\)
b)\(\frac{3^{10}\times11+3^{10}\times5}{3^9\times2^4}\)
c)\(\left(1:\frac{1}{7}\right)^2[\left(2^2\right)^3:2^5]\times\frac{1}{49}\)
d)\(\frac{4^6\times3^5-2^{12}\times3^6}{2^{12}\times9^3+8^4\times3^5}\)
Tính nhanh giá trị biểu thức :
\(\frac{1\times3\times5+2\times6\times10+4\times10\times12+7\times21\times35}{1\times5\times7+2\times10\times14+4\times20\times28+7\times35\times49}\)
1 x 3 x 5 + 2 x 6 x 10 + 4 x 10 x 12 + 7 x 21 x 35 / 1 x 5 x 7 + 2 x 10 x 14 + 4 x 20 x 28 + 7 x 35 x 49
= 3 / 7 + 6 / 14 + 10 x 2 x 6 / 10 x 2 x 28 + 21 / 49
= 3 / 7 + 6 / 14 + 6 / 28 + 21 / 49
= 3 / 7 + 6 / 14 + 3 / 14 + 3 / 7
= ( 3 / 7 + 3 / 7 ) + ( 6 / 14 + 3 / 14 )
= 6 / 7 + 9 14
= 12 / 14 + 9 / 14
= 21 / 14
nho hem
lm dau tien lun do
dung 100% nha
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