\(a)\left(2x+5\right)\left(2x-7\right)-\left(-4x-3\right)^2=16\\ \Leftrightarrow4x^2-14x+10x-35-\left(16x^2+24x-9\right)=16\\ \Leftrightarrow-12x^2-28x-44=16\\ \Leftrightarrow-12x^2-28x-60=0\\ \Leftrightarrow3x^2+7x+15=0\\ \Delta=b^2-4ac=7^2-4.3.15=-131< 0\)
Vậy phương trình vô nghiệm
\( b)(8x^2 + 3)(8x^2 - 3) - (8x^2 - 1)^2 = 22\)
\(\Leftrightarrow64x^4-9-\left(64x^4-16x^2+1\right)=22\\ \Leftrightarrow-10+16x^2=22\\ \Leftrightarrow16x^2=32\\ \Leftrightarrow x^2=2\\ \Leftrightarrow x=\pm\sqrt{2}\)
Vậy \(x=\sqrt{2},x=-\sqrt{2}\)
\(c)49x^2+14x+1=0\\ \Leftrightarrow\left(7x+1\right)^2=0\\ \Leftrightarrow7x+1=0\\ \Leftrightarrow7x=-1\)
\(\Leftrightarrow\)\(x=-\dfrac{1}{7}\)
Vậy \(x=-\dfrac{1}{7}\)
\(\Leftrightarrow\)\(x=-\dfrac{1}{7}\)