tìm x biết
1.(5x-1^2) – (5x -4)(5x+ 4)=7
2.(4x + 1)^2 – (2x + 3)^2 + 5 (x + 2 )^2 + 3(x – 2 )(x + 2 )= 500
3.(x-3)( x^2 + 3 x + 9 )+ x (x + 2) (2 – x )= 1
4.(x + 1 )^3- ( x -1) ^3 – 6 (x – 1)^ 2 = -10
5.(x+ 2)^ 2 – x (x – 1)( x + 1) = 6x^2 – 5x + 3
Đáp án:
1.(5x-1^2) – (5x -4)(5x+ 4)=7
⇔25x²-10x+1-25x²+16=7
⇔-10x+17=7
⇔-10x=-10
⇔x=1
2.(4x + 1)^2 – (2x + 3)^2 + 5 (x + 2 )^2 + 3(x – 2 )(x + 2 )= 500
⇔16x²+8x+1-4x²-12x-9+5(x²+4x+4)+3(x²-4)=500
⇔12x²-3x-8+5x²+20x+20+3x²-12=500
⇔20x²+17x=500
3.(x-3)( x^2 + 3 x + 9 )+ x (x + 2) (2 – x )= 1
⇔x³+3x²+9x-3x²-9x-27+4x-x³-1=0
⇔4x-28=0
⇔x=7
5.(x+ 2)^ 2 – x (x – 1)( x + 1) = 6x^2 – 5x + 3
⇔x²+4x+4-x(x²-1) -6x^2 +5x -3=0
⇔-5x²+9x+1-x³+x=0
⇔-x³-4x²+9x+1=0
Giải thích các bước giải:
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