\(Tính:\\ \frac{\left(2m-10\right)^2}{\left(m+5\right)^2+1}\)
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\(A=\dfrac{1}{2}-\left(\dfrac{1}{2}\right)^2-\left(\dfrac{1}{2}\right)^3-...-\left(\dfrac{1}{2}\right)^{10}\\ \\2A=1-\dfrac{1}{2}-\left(\dfrac{1}{2}\right)^2-...-\left(\dfrac{1}{2}\right)^9\\ 2A-A=\left[1-\dfrac{1}{2}-\left(\dfrac{1}{2}\right)^2-...-\left(\dfrac{1}{2}\right)^9\right]-\left[\dfrac{1}{2}-\left(\dfrac{1}{2}\right)^2-\left(\dfrac{1}{2}\right)^3-...-\left(\dfrac{1}{2}\right)^{10}\right]\\ A=1-\dfrac{1}{4}+\left(\dfrac{1}{2}\right)^{10}\)
\(M=\left[0,\left(5\right).0,\left(2\right)\right]:\left(3\frac{1}{3}:\frac{33}{25}\right)-\left[0,4.1,\left(3\right)\right]:1,\left(3\right)=\left(\frac{5}{9}\cdot\frac{2}{9}\right):\left(\frac{10}{3}\cdot\frac{25}{33}\right)-\left(\frac{2}{5}\cdot\frac{4}{3}\right):\frac{4}{3}\)
=\(\frac{10}{81}:\frac{250}{99}-\frac{8}{15}\cdot\frac{3}{4}=\frac{10}{99}\cdot\frac{99}{250}-\frac{2}{5}=\frac{1}{25}-\frac{10}{25}=-\frac{9}{25}\)
`(2m-10)^2/((m+5)^2+1)`
`=(2m-10)^2/(m^2+10m+26)-404+404`
`=(4m^2-40m+100)/(m^2+10m+26)-404+404`
`=(4m^2-40m+100-404m^2-4040m-10504)/(404[(m+5)^2+1])+404`
`=(-400m^2-4080m-10404)/(404[(m+5)^2+1])+404`
`=(-(400m^2+4080m+10404))/(404[(m+5)^2+1])+404`
`=(-(20m+102)^2)/(404[(m+5)^2+1])+404<=404`
Dấu "=" xảy ra khi `20m+102=0<=>m=(-51)/10`
Bài này giải kiểu lớp 8 thì nó cực kì vô duyên:
\(P=\dfrac{4m^2-40m+100}{m^2+10m+26}=\dfrac{404\left(m^2+10m+26\right)-4\left(100m^2+1020m+2601\right)}{m^2+10m+26}\)
\(P=404-\dfrac{4\left(10m+51\right)^2}{\left(m+5\right)^2+1}\le404\)
\(P_{max}=404\) khi \(m=-\dfrac{51}{10}\)
Xét số hạng tổng quát:
\(k^4+\frac{1}{4}=\left(k^4+2\cdot\frac{1}{2}\cdot k^2+\frac{1}{4}\right)-k^2\)
= \(\left(k^2+\frac{1}{2}\right)^2-k^2\)= \(\left(k^2-k+\frac{1}{2}\right)\left(k^2+k+\frac{1}{2}\right)\)
Thay k từ 1 đến 2014 , ta được
M=
\(\frac{\left(2+\frac{1}{2}\right)\left(6+\frac{1.}{2}\right)...\left(4054182+\frac{1}{2}\right)\left(4058210+\frac{1}{2}\right)}{\frac{1}{2}\cdot\left(2+\frac{1}{2}\right)...\left(4050156+\frac{1}{2}\right)\left(4054182+\frac{1}{2}\right)}\)=\(\frac{4058210+\frac{1}{2}}{\frac{1}{2}}=8116421\)