Question

Bài 4: Tìm x

a, (x + 1)² - x (x - 3) = 2x + 3

b, (x + 2) (x - 3 ) - (x - 3)² = 15

c, (x + 1)³ -(x³ + 3x² + 2x - 3) = 0

Answer 1

\(a,\Leftrightarrow x^2+2x+1-x^2+3x-2x=3\\ \Leftrightarrow3x=2\Leftrightarrow x=\dfrac{3}{2}\\ b,\Leftrightarrow x^2-x-6-x^2+6x-9=15\\ \Leftrightarrow5x=30\Leftrightarrow x=6\\ c,\Leftrightarrow x^3+3x^2+3x+1-x^3-3x^2-2x+3=0\\ \Leftrightarrow x=-4\)

Answer 2

a) \(\left(x+1\right)^2-x\left(x-3\right)=2x+3\Rightarrow x^2+2x+1-x^2+3x=2x+3\)

\(\Rightarrow3x=2\Rightarrow x=\dfrac{2}{3}\)

Answer 3

b) \(\left(x+2\right)\left(x-3\right)-\left(x-3\right)^2=15\Rightarrow x^2-3x+2x-6-\left(x^2-6x+9\right)=15\)

\(\Rightarrow5x=30\Rightarrow x=6\)

Answer 4

c) \(\left(x+1\right)^3-\left(x^3+3x^2+2x-3\right)=0\)

   \(\Rightarrow x^3+3x^2+3x+1-x^3-3x^2-2x+3=0\)

   \(\Rightarrow x=-4\)