A = \(\frac{a^5+a^6+a^7+a^8}{a^{-5}+a^{-6}+a^{-7}+a^{-8}}\)
Tinh bieu thuc A tai a=2015
H24
Những câu hỏi liên quan
\(\frac{a^5+a^6+a^7+a^8}{a^{-5}+a^{-6}+a^{-7}+a^{-8}}\)
Rut gon bieu thuc tren.
Tinh hop ly cac gia tri bieu thuc sau
a) \(4\frac{8}{23}+5\frac{7}{8}-9\frac{8}{23}\)
b)\(6\frac{3}{8}+5\frac{1}{2}\)
Tinh gia tri cua bieu thuc:
a, 4+11/8-5/6=
b, (1/2+4/7)-(3/7-3/10)=
\(4+\frac{11}{8}-\frac{5}{6}=\frac{96+33-20}{24}=\frac{109}{24}\)
\(\left(\frac{1}{2}+\frac{4}{7}\right)-\left(\frac{3}{7}-\frac{3}{10}\right)=\frac{1}{2}+\frac{4}{7}-\frac{3}{7}+\frac{3}{10}\)
\(\left(\frac{1}{2}+\frac{3}{10}\right)+\left(\frac{4}{7}-\frac{3}{7}\right)=\frac{4}{5}+\frac{1}{7}=\frac{28+5}{35}=\frac{33}{35}\)
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ban Chitanda Eru oi to bao nhung ma nhan voi bao nhieu ma ra duoc 96
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cho a=-47;b=23:c=-15 tinh gia tri bieu thuc
a) a+11-a-59
b) a-b-22+25+b
c) -a-18+c+18-c+b
d) b-5+a-6-c+7-a+8
cho bieu thuc A = \(\left(\frac{x-\sqrt{x}}{\sqrt{x}-1}+1\right):\left(\frac{x+\sqrt{x}}{\sqrt{x}+1}\right)\)
a. tim x de bieu thuc A co nghia ?rut gon A ?
b. tinh gia tri cua bieu thuc A tai x=7+4√3
a. A có nghĩa khi \(\left\{{}\begin{matrix}x\ge0\\\sqrt{x}-1\ne\\\frac{x+\sqrt{x}}{\sqrt{x}+1}\ne0\end{matrix}\right.0\Leftrightarrow\left\{{}\begin{matrix}x\ge0\\x\ne1\end{matrix}\right.\)
A\(=\frac{x-\sqrt{x}+\sqrt{x}-1}{\sqrt{x}-1}.\frac{\sqrt{x}+1}{x+\sqrt{x}}\)\(=\frac{x-1}{\sqrt{x}-1}.\frac{\sqrt{x}+1}{\sqrt{x}\left(\sqrt{x}+1\right)}=\frac{\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}{\sqrt{x}-1}.\frac{\sqrt{x}+1}{\sqrt{x}\left(\sqrt{x}+1\right)}=\frac{\sqrt{x}+1}{\sqrt{x}}\)
b. \(x=7+4\sqrt{3}\Rightarrow\)A = \(\frac{\sqrt{7+4\sqrt{3}}+1}{\sqrt{7+4\sqrt{3}}}=\frac{\sqrt{\left(2+\sqrt{3}\right)^2}+1}{\sqrt{\left(2+\sqrt{3}\right)^2}}=\frac{3+\sqrt{3}}{2+\sqrt{3}}\)
Tinh gia tri bieu thuc: A=1/2*5+1/5*8+1/8*11+....+1/2012*2015
A=1/2*5+1/5*8+1/8*11+...+1/2012*1015
=1/3*(1/2-1/5+1/5-1/8+1/8-1/11+...+1/2012-1/2015)
=1/3*(1/2-1/1/2015)
=1/3*2013/4030
=671/4030
vậy A=671/4030
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cho bieu thuc A =\(\left(\frac{x-\sqrt{x}}{\sqrt{x}-1}+1\right):\left(\frac{x+\sqrt{x}}{\sqrt{x}+1}\right)\)
(x≥0;x≠1)
a. tim x de bieu thuc A co nghia ?rut gon A ?
b. tinh gia tri bieu thuc A tai x=7+4√3
a/ Ta có: A=\(\left(\frac{x-\sqrt{x}}{\sqrt{x}-1}+1\right):\left(\frac{x+\sqrt{x}}{\sqrt{x}+1}\right)=\left(\frac{\sqrt{x}\left(\sqrt{x}-1\right)}{\sqrt{x}-1}+1\right):\left(\frac{\sqrt{x}\left(\sqrt{x}+1\right)}{\sqrt{x}+1}\right)\)
\(=\left(\sqrt{x}+1\right):\left(\sqrt{x}\right)=\frac{\sqrt{x}+1}{\sqrt{x}}\)
b/ Ta có :\(x=7+4\sqrt{3}=3+4\sqrt{3}+4=\left(\sqrt{3}+2\right)^2
\)
\(\Rightarrow\sqrt{x}=|\sqrt{3}+2|=\sqrt{3}+2\)
Thay x vào A ta có:
A\(=\frac{\sqrt{x}+1}{\sqrt{x}}=\frac{\sqrt{3}+2+1}{\sqrt{3}+2}=\frac{\sqrt{3}+3}{\sqrt{3}+2}=\frac{\left(\sqrt{3}+3\right)\left(2-\sqrt{3}\right)}{\left(2-\sqrt{3}\right)\left(2+\sqrt{3}\right)}=\frac{3-\sqrt{3}}{1}=3-\sqrt{3}\)
Tinh gia tri bieu thuc bang cach thuan tien nhat :
A= 1/10 x 2/9 x 3/8 x 4/7 x 5/6 x 6/5 x 7/4 x 8/3 x 9/2
cho bieu thuc A=\(\left(\frac{x-\sqrt{x}}{\sqrt{x}+1}+1\right):\left(\frac{x+\sqrt{x}}{\sqrt{x}+1}\right)\)
(x≥0;x≠1)
a.Tim x de bieu thuc A co nghia ? rut gon A ?
b. Tinh gia tri cua bieu thuc A tai x=7=4√3