\(=-\dfrac{3}{2}x^3+3-2x+\dfrac{5}{2}x^2\)

27 x 3 + 36 : 4 : 3 x 5 - 25 : 5 x 4

= 81 + 36: 4 : 3 x 5 - 5 x 4

= 81 + 9 : 3 - 20

= 81 + 3 - 20

= 84 - 20

= 64

27 x 3 + 36 : 4 : 3 x 5 - 25 : 5 x 4

= 81 + 36: 4 : 3 x 5 - 5 x 4

= 81 + 9 : 3 - 20

= 81 + 3 - 20

= 84 - 20

= 64

cậu đang khen hay đang đe doạ vậy

5 x 3 + 5 x 4 + 5 x 2 + 5

= 5 x 3 + 5 x 4 + 5 x 2 + 5 x 1

= 5 x ( 3 + 4 + 2 + 1 )

= 5 x 10

= 50

  5 x 3 + 5 x 4 + 5 x 2 + 5

 = 5 x (3 + 4 + 2) + 5

= 5 x 9 + 5

= 45 + 5

= 50

=5x(3+4+2+1)

=5x10

=50

\(B=1.3+3.5+5.7+....+27.29+29.31\)

\(6B=1.3.6+3.5.6+5.7.6+....+27.29.6+29.31.6\)

\(6B=1.3.\left(5+1\right)+3.5.\left(7-1\right)+5.7.\left(9-3\right)+...+27.29.\left(31-25\right)+29.31.\left(33-27\right)\)

\(6B=1.3.5+3+3.5.7-1.3.5+5.7.9-3.5.7+...+27.29.31-25.27.29+29.31.33-27.29.31\)

\(6B=3+29.31.33\)

\(B=\frac{3+29.21.33}{6}=4945\)

`@` `\text {Ans}`

`\downarrow`

`a)`

Thu gọn:

`P(x)=`\(5x^4 + 3x^2 - 3x^5 + 2x - x^2 - 4 +2x^5\)

`= (-3x^5 + 2x^5) + 5x^4 + (3x^2 - x^2) + 2x - 4`

`= -x^5 + 5x^4 + 2x^2 + 2x - 4`

`Q(x) =`\(x^5 - 4x^4 + 7x - 2 + x^2 - x^3 + 3x^4 - 2x^2\)

`= x^5 + (-4x^4 + 3x^4) - x^3 + (x^2 - 2x^2) + 7x - 2`

`= x^5 - x^4 - x^3 - x^2 + 7x - 2`

`@` Tổng:

`P(x)+Q(x)=`\((-x^5 + 5x^4 + 2x^2 + 2x - 4) + (x^5 - x^4 - x^3 - x^2 + 7x - 2)\)

`= -x^5 + 5x^4 + 2x^2 + 2x - 4 + x^5 - x^4 - x^3 - x^2 + 7x - 2`

`= (-x^5 + x^5) - x^3 + (5x^4 - x^4) + (2x^2 - x^2) + (2x + 7x) + (-4-2)`

`= 4x^4 - x^3 + x^2 + 9x - 6`

`@` Hiệu:

`P(x) - Q(x) =`\((-x^5 + 5x^4 + 2x^2 + 2x - 4) - (x^5 - x^4 - x^3 - x^2 + 7x - 2)\)

`= -x^5 + 5x^4 + 2x^2 + 2x - 4 - x^5 + x^4 + x^3 + x^2 - 7x + 2`

`= (-x^5 - x^5) + (5x^4 + x^4) + x^3 + (2x^2 + x^2) + (2x - 7x) + (-4+2)`

`= -2x^5 + 6x^4 + x^3 + 3x^2 - 5x - 2`

`b)`

`@` Thu gọn:

\(H (x) = ( 3x^5 - 2x^3 + 8x + 9) - ( 3x^5 - x^4 + 1 - x^2 + 7x)\)

`= 3x^5 - 2x^3 + 8x + 9 - 3x^5 + x^4 - 1 + x^2 - 7x`

`= (3x^5 - 3x^5) + x^4 - 2x^3 - x^2 + (8x + 7x) + (9+1)`

`= x^4 - 2x^3 - x^2 + 15x + 10`

\(R( x) = x^4 + 7x^3 - 4 - 4x ( x^2 + 1) + 6x\)

`= x^4 + 7x^3 - 4 - 4x^3 - 4x + 6x`

`= x^4 + (7x^3 - 4x^3) + (-4x + 6x) - 4`

`= x^4 + 3x^3 + 2x - 4`

`@` Tổng:

`H(x)+R(x)=` \((x^4 - 2x^3 - x^2 + 15x + 10)+(x^4 + 3x^3 + 2x - 4)\)

`= x^4 - 2x^3 - x^2 + 15x + 10+x^4 + 3x^3 + 2x - 4`

`= (x^4 + x^4) + (-2x^3 + 3x^3) - x^2 + (15x + 2x) + (10-4)`

`= 2x^4 + x^3 - x^2 + 17x + 6`

`@` Hiệu: 

`H(x) - R(x) =`\((x^4 - 2x^3 - x^2 + 15x + 10)-(x^4 + 3x^3 + 2x - 4)\)

`=x^4 - 2x^3 - x^2 + 15x + 10-x^4 - 3x^3 - 2x + 4`

`= (x^4 - x^4) + (-2x^3 - 3x^3) - x^2 + (15x - 2x) + (10+4)`

`= -5x^3 - x^2 + 13x + 14`

`@` `\text {# Kaizuu lv u.}`

\(\frac{1}{1.3}+\frac{1}{3.5}+\frac{1}{5.7}+\frac{1}{7.9}\)

\(=\frac{1}{2}.\left(\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}\right)\)

\(=\frac{1}{2}.\left(\frac{1}{1}-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}\right)\)

\(=\frac{1}{2}.\left(1-\frac{1}{9}\right)\)

\(=\frac{1}{2}.\frac{8}{9}\)

\(=\frac{4}{9}\)

#)Giải :

\(S=\frac{1}{1.3}+\frac{1}{3.5}+\frac{1}{5.7}+\frac{1}{7.9}\)

\(\Rightarrow2S=\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}\)

\(\Rightarrow2S=1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}\)

\(\Rightarrow2S=1-\frac{1}{9}=\frac{8}{9}\)

\(S=\frac{8}{9}:2=\frac{4}{9}\)

             #~Will~be~Pens~#

S=\(\frac{1}{1×3}+\frac{1}{3×5}+\frac{1}{5×7}+\frac{1}{7×9}\)

S=\(\frac{1.2}{\left(1.3\right).2}+\frac{1.2}{\left(3.5\right).2}+\frac{1.2}{\left(5.7\right).2}+\frac{1.2}{\left(7.9\right).2}\)

S=\(\frac{1}{2}.\left(\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}\right)\)

S= \(\frac{1}{2}.\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}\right)\)

S= \(\frac{1}{2}.\left(1-\frac{1}{9}\right)\)

S= 1/2 . 8/9

S = 4/9

Lưu ý : "." có nghĩa là dấu nhân , lên cấp 2 bạn sẽ được học  

\(\frac{1}{3}.\frac{5}{2}.2.\frac{2}{5}.\frac{4}{8}.3\)

\(=\left(\frac{1}{3}.3\right).\left(\frac{5}{2}.\frac{2}{5}\right).\left(2.\frac{4}{8}\right)\)

\(=1.1.1=1\)

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