2.5 - 36:32
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a , = 123+39-23 =(123-23) +39 =100+39 =139
b, = (64+36).32 = 100.32 =3200
c, =62.4 +5.2(5-1) =62.4 + 40 = 36.4+40 =144+40 +184
d, đề sao sao ấy nhể k rõ đề lm
a. ( 123 + 39 ) -23
= 123 + 39 - 23
= ( 123 - 23 ) + 39
= 100 + 39
= 139
b. 64 . 32 + 32 . 36
= 32 . ( 64 + 36 )
= 32 . 100
= 3200
c. 62 .4 + 2.52 -10
= 36 . 4 + 2 . 25 -10
= 114 + 50 - 10
= 114 + 40
= 151
d.( 5 . 23 - 2 . 3 2 ) : 11 +5 - I-5I
= ( 5 . 8 - 2 . 9 ) : 11 + 5 - 5
= ( 40 -18 ) : 11 + 0
= 22 : 11 + 0
= 2 + 0
= 2
\(36:3^2-2.5^3\)
\(\Rightarrow36:9-2.125\)
\(\Rightarrow4-250\)
\(\Rightarrow-246\)
TK
S=1.4+2.5+3.6+4.7+....+n.(n+3) S = 1. ( 2 + 2 ) + 2. ( 3 + 2 ) + 3. ( 4 + 2 ) + . . . + n . [ ( n + 1 ) + 2 ] S = 1.2 + 2.3 + 3.4 + . . . . + n . ( n + 1 ) + ( 1.2 + 2.2 + 3.2 + . . . . + n .2 ) Đặt A = 1.2 + 2.3 + 3.4 + . . . . + n . ( n + 1 ) 3 A = 1.2.3 + 2.3. ( 4 − 1 ) + . . . . + n . ( n + 1 ) . [ ( n + 2 ) − ( n − 1 ) 3 A = 1.2.3 + 2.3.4 − 1.2.3 + . . . . + n . ( n + 1 ) . ( n + 2 ) − ( n − 1 ) . n . ( n + 1 ) 3 A = n . ( n + 1 ) . ( n + 2 ) A = [ n . ( n + 1 ) . ( n + 2 ) ] : 3 S = [ n . ( n + 1 ) . ( n + 2 ) ] : 3 + 2. ( 1 + 2 + 3 + . . . + n ) S = [ n . ( n + 1 ) . ( n + 2 ) ] : 3 + 2. n . ( n + 1 ) : 2 S = n . ( n + 1 ) . ( n + 2 ) : 3 + n . ( n + 1 ) S = n . ( n + 1 ) . [ ( n + 2 ) : 3 + 1 )
D = 1^2 + 2^2 + 3^2 + ... + n^2
= 1.( 2 - 1 ) + 2.( 3-1 ) + 3.( 4-1 ) + .... + n.[ ( n+ 1) - 1 ]
= 1.2 - 1 + 2.3 - 2 + 3.4 - 3 + .... + n.( n+1 ) - n
= [ 1.2 + 2.3 + 3.4 + ..... + n.( n + 1 ) ] - ( 1 + 2 + 3 + .... + n )
= { [ n.( n+1 ).( n+2 )] /3 } - { [ n.( n+1)] /2 }
= { n(n+1)(2n+1) }/ 6
Vậy.........
\(36:\left\{180:\left[2\cdot5^2-\left(5^3-3\cdot5\cdot7\right)\right]\right\}\)
\(=36:\left\{180:\left[2\cdot25-\left(125-15\cdot7\right)\right]\right\}\)
\(=36:\left\{180:\left[50-\left(125-105\right)\right]\right\}\)
\(=36:\left[180:\left(50-20\right)\right]\)
\(=36:\left(180:30\right)\)
\(=36:6\)
\(=6\)
\(=\dfrac{36}{180:\left[2\cdot25-5^3+15\cdot7\right]}=\dfrac{36}{180:30}=\dfrac{36}{6}=6\)
S=6/2*5+6/5*8+...+6/29*32
=6/3*(3/2*5+3/5*8+...+3/29*32)
=2*(1/2-1/5+1/5-1/8+...+1/29-1/32)
=2*(1/2-1/32)=2*15/32
=15/16<1
S=6/2*5+6/5*8+...+6/29*32,c
=6/3*(3/2*5+3/5*8+...+3/29*32)
=2*(1/2-1/5+1/5-1/8+...+1/29-1/32)
=2*(1/2-1/32)
=2*15/32
=15/16<1
\(=\left(\dfrac{19}{42}+\dfrac{23}{42}\right)+\left(\dfrac{1}{37}+\dfrac{36}{37}\right)+10\)
=12
=10-36.9
=10-324
=-314