Question

1. Tìm x: 

( 3x + 2 ) ( 2x + 9 ) - ( x + 2 ) ( 6x + 1 ) = ( x + 1 ) - ( x- 6 )

2. Tính giá trị biểu thức:

A= x⁵ - 15x⁴ + 16x³ - 29x² + 13x tại x = 14

Answer 1

1. \(< =>\left(6x^2+31x+18\right)-\left(6x^2+13x+2\right)=x+1-a+6\)

      \(< =>6x^2+31x+18-6x^2-13x-2=7\)

       \(< =>18x+16=7\)

        \(< =>18x=7-16\)

           \(< =>18x=-9\)

           \(< =>x=-\frac{9}{18}=-\frac{1}{2}\)

Answer 2

2. vì x=14 nên x+1=15 ; x+2 = 16;    2x + 1 =29;   x-1=13

thay  vào A ta được

\(A=x^5-\left(x+1\right)x^4+\left(x+2\right)x^3-\left(2x+1\right)x^2+\left(x-1\right)x\)

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

\(A=-x=-14\)

Answer 3

2. vì x=14 nên x+1=15 ; x+2 = 16;    2x + 1 =29;   x-1=13

thay  vào A ta được

$A=x^5-\left(x+1\right)x^4+\left(x+2\right)x^3-\left(2x+1\right)x^2+\left(x-1\right)x$A=x5−(x+1)x4+(‍x+2)x3−(2x+1)x2+(x−1)x

$A=x^5-x^5-x^4+x^4+2x^3-2x^3-x^2+x^2-x$A=x5−x5−x4+x4‍+2x3−2x3−x2+x2−x

$A=-x=-14$