1^2+2^2+3^2+.......+49^2+50^2
làm hộ mình nhá
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(50-1):1+1=50 số
=(50-49)+(48-47)+...+(4-3)+(2-1). Ta có 25 cặp số
=1+1+1+....+1
=1.25
=25
\(\left(\dfrac{3}{20}+\dfrac{1}{2}-\dfrac{1}{15}\right)\times\dfrac{12}{49}\)
\(=\left(\dfrac{3}{20}+\dfrac{10}{20}-\dfrac{1}{15}\right)\times\dfrac{12}{49}\)
\(=\left(\dfrac{13}{20}-\dfrac{1}{15}\right)\times\dfrac{12}{49}\)
\(=\left(\dfrac{39}{60}-\dfrac{4}{60}\right)\times\dfrac{12}{49}\)
\(=\dfrac{35}{60}\times\dfrac{12}{49}\)
\(=\dfrac{35\times12}{60\times49}\)
\(=\dfrac{1}{7}\)
_HT_
50 x 125 x 2 x 8 x 805
(50 . 2).(125. 8). 805
100. 1000 . 805
100000. 805
80500000
chúc bạn học tốt!!!
50 x 125 x 2 x 8 x 805
= ( 50 x 2 ) x ( 125 x 8 ) x 805
= 100 x 1000 x 805
= 100 000 x 805
= 80 500 000
_HT_
\(a,\Rightarrow n-2+5⋮n-2\\ \Rightarrow n-2\inƯ\left(5\right)=\left\{-5;-1;1;5\right\}\\ \Rightarrow n\in\left\{-3;1;3;7\right\}\\ b,\Rightarrow2\left(n-4\right)+13⋮n-4\\ \Rightarrow n-4\inƯ\left(13\right)=\left\{-13;-1;1;13\right\}\\ \Rightarrow n\in\left\{-9;3;5;17\right\}\\ c,\Rightarrow6n-9⋮3n+1\\ \Rightarrow2\left(3n+1\right)-12⋮3n+1\\ \Rightarrow3n+1\inƯ\left(12\right)=\left\{-12;-6;-4;-3;-2;-1;1;2;3;4;6;12\right\}\\ \Rightarrow n\in\left\{-1;0;1\right\}\left(n\in Z\right)\\ d,\Rightarrow n^2+2n-n-2+3⋮n+2\\ \Rightarrow n\left(n+2\right)-\left(n+2\right)+3⋮n+2\\ \Rightarrow n+2\inƯ\left(3\right)=\left\{-3;-1;1;3\right\}\\ \Rightarrow n\in\left\{-5;-3;-1;1\right\}\)
\(\left(3\frac{1}{2}-0,5\right)x\frac{1}{27}+1\frac{1}{3}\)
= \(3x\frac{1}{27}+1\frac{1}{3}\)
= \(\frac{1}{9}+\frac{4}{3}\)
= \(\frac{13}{9}\)
mình ko làm hộ đâu nhá