a) 2x(x+5)= (x+3)2+(x+1)2+20
\(\Leftrightarrow\) 2x2+10x = x2 + 6x +9 + x2 + 2x + 1 + 20
\(\Leftrightarrow\) 2x = 30 \(\Leftrightarrow\) x= 15
b) (2x-2)2 = (x+1)2 +3(x-2)(x+5)
\(\Leftrightarrow\) 4x2 - 8x +4 = x2 + 2x + 1 + 3x2 + 9x - 30
\(\Leftrightarrow\) 4 - 8x = 11x - 29
\(\Leftrightarrow\) 19x = 33 \(\Leftrightarrow\) x = \(\frac{33}{19}\)
a, 2x(x+5)=(x+3)2 +(x+1)2+20
2x2+10x=x2+6x+9+x2+2x+1+20
2x=30
x=15
các câu sau tương tự cách làm nhân ra rồi chuyển về để trừ
c) (x-1)2 + (x+3)2 = 2(x-2)(x+1) + 38
\(\Leftrightarrow\) x2 - 2x + 1 + x2 + 6x +9 = 2x2 - 2x - 4 + 38
\(\Leftrightarrow\) 2x2 + 4x + 10 = 2x2 - 2x + 34
\(\Leftrightarrow\) 6x = 24 \(\Leftrightarrow\) x = 4 
d) ( x+2 )2 - ( x-2)3 = 12x(x-1)-8
\(\Leftrightarrow\) x2 + 4x + 4 - ( x3 - 6x2 + 12x - 8) = 12x2 - 12x -8
\(\Leftrightarrow\) -x3 + 7x2 - 8x + 12 = 12x2 - 12x -8
\(\Leftrightarrow\) -x3 + 4x + 20 - 5x2 =0
\(\Leftrightarrow\) (x-2)(x+2)(x+5) =0
\(\Leftrightarrow\) x-2 = 0 ; x+2=0 ; x+5=0
\(\Leftrightarrow\) x=2 ; x=-2 ; x=-5 T_T
