1+1+2+2+3+3+4+4+...+5+5+6+6

do 4 và 5 cách nhau 1 đơn vị nên dấu " ... " chỉ là đánh lừa

= 1²+2²3²+4²+5²+6²

= 1+4+9+16+25+36

= (1+9) + (4+16) + 25+35+1

= 10 + 20 + 60 + 1

= 30 + 60 + 1

= 90 + 1

= 91

Sai r bn

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

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

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

= x²-5x-2x³+x⁴+1+(-5x³)-3+8x⁴+x²

=(x²+x²)+(-2x³-5x³)+(x⁴+8x⁴)-5x+(1-3)

=2x²+(-7x³)+9x⁴-5x+(-2)

làm nick mằm chi nữa

không giúp thì thôi

a: \(A\left(2\right)=2^5-2\cdot2^4+5\cdot2-3=32-32+10-3=7\)

\(B\left(-1\right)=-\left(-1\right)^5+3\cdot\left(-1\right)^3+5\cdot\left(-1\right)+11=1-3-5+11=4\)

b: Ta có: A(x)+B(x)

\(=x^5-2x^4+5x-3-x^5+3x^3+5x+11\)

\(=-2x^4+3x^3+10x+8\)

Ta có: A(x)-B(x)

\(=x^5-2x^4+5x-3+x^5-3x^3-5x-11\)

\(=2x^5-2x^4-3x^3-14\)

1) x-2x-3x-4x-5x=-13x thay x=-8 => -13x=(-8).(-13)=104

2)(x+1)-2(x+1)-3(x+1)-4(x+1)-5(x+1)=-13(x+1) thay x=-8 => -13(x+1)=(-13).(-7)-91

1) Thay x = -8 , ta có ;

(-8) - 2 x (-8) - 3 x (-8) - 4 x (-8 ) - 5 x (-8) = 104

2) Thay x = -8 , ta có ;

(-8 + 1)-2(-8 + 1)-3( -8 + 1 )- 4( -8 + 1 ) - 5( -8 + 1 ) =91

Đúng thì tick ko đúng thì thôi 

\(\dfrac{1}{7}\times\dfrac{21}{8}-\dfrac{3}{8}\times\dfrac{1}{7}-\dfrac{1}{7}\times\dfrac{2}{8}\\ =\dfrac{1}{7}\times\left(\dfrac{21}{8}-\dfrac{3}{8}-\dfrac{2}{8}\right)\\ =\dfrac{1}{7}\times\dfrac{16}{8}\\ =\dfrac{1}{7}\times2\\ =\dfrac{2}{7}\)

\(\dfrac{1}{7}\times\dfrac{21}{8}-\dfrac{3}{8}\times\dfrac{1}{7}-\dfrac{1}{7}\times\dfrac{2}{8}\)

=\(\dfrac{1}{7}\times\left(\dfrac{21}{8}-\dfrac{3}{8}-\dfrac{2}{8}\right)\)

=\(\dfrac{1}{7}\times2\)

=\(\dfrac{2}{7}\)

1) 2x – (3 – 5x) = 4( x +3)

<=>2x-3+5x=4x+12

<=>2x-3+5x-4x-12=0

<=>3x-15=0

<=>x=5

2) 5(2x-3) - 4(5x-7) =19 - 2(x+11)

<=>10x-15-20x+28=19-2x-22

<=>10x-15-20x+28-19+2x+22=0

<=>-8x+16=0

<=>x=2