III.
a) \(\left(5x+1\right)^2-\left(5x+3\right)\left(5x-3\right)=30\)
\(\Leftrightarrow\)\(25x^2+10x+1-25x^2+9=30\)
\(\Leftrightarrow\)\(10x=20\)
\(\Leftrightarrow\)\(x=2\)
Vậy...
b) \(\left(3x-1\right)^2+2\left(x+3\right)^2+11\left(x+1\right)\left(1-x\right)=6\)
\(\Leftrightarrow\)\(9x^2-6x+1+2x^2+12x+18+11-11x^2=6\)
\(\Leftrightarrow\)\(6x=-24\)
\(\Leftrightarrow\)\(x=-4\)
Vậy....
II.
a) mk chỉnh lại đề câu a
\(a^2-2a+1=\left(a-1\right)^2\)
b) \(1-4a+4a^2=\left(1-2a\right)^2\)
c) \(a^2+9-6a=\left(a-3\right)^2\)
d) \(25a^2-20ab+4b^2=\left(5a-2b\right)^2\)