Question

bt1: tìm x, biết

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

b) (x + 1)³ - (x + 3)(x² - 3x + 9) = (x - 3)² + 3(2x + 1)² - (x³ - 5x + 1)

Answer 1

a: \(\Leftrightarrow4x^2+12x+9+x^2-1=5\left(x^2+4x+4\right)-\left(x^2-4x-5\right)+x^2+8x+16\)

\(\Leftrightarrow5x^2+12x+8=5x^2+20x+20-x^2+4x+5+x^2+8x+16\)

\(\Leftrightarrow5x^2+12x+8=5x^2+32x+41\)

=>12x+8=32x+41

=>-20x=33

hay x=-33/20

b: \(\Leftrightarrow x^3+3x^2+3x+1-x^3-27=x^2-6x+9+3\left(4x^2+4x+1\right)-x^3+5x-1\)

\(\Leftrightarrow3x^2+3x-26=-x^3+x^2-x+8+12x^2+12x+3\)

\(\Leftrightarrow3x^2+3x-26=-x^3+13x^2+11x+11\)

\(\Leftrightarrow x^3-10x^2-8x-36=0\)

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