Question

Помогите пожалуйста

Answer 1

$1)7x^{2} -9x+2=0\\\\D=(-9)^{2}-4*7*2=81-56=25=5^{2}\\\\x_{1}=\frac{9+5}{14}=1\\\\x_{2}=\frac{9-5}{14}=\frac{2}{7}\\\\Otvet:\boxed{1;\frac{2}{7}}\\\\\\2)5x^{2}=12x\\\\5x^{2}-12x=0\\\\x(5x-12)=0\\\\\left[\begin{array}{ccc}x_{1}=0 \\5x-12=0\end{array}\right\\\\\\\left[\begin{array}{ccc}x_{1}=0 \\x_{2}=2,4 \end{array}\right\\\\Otvet:\boxed{0;2,4}$

$3)7x^{2} -28=0\\\\7x^{2}=28\\\\x^{2}=4\\\\x_{1}=2\\\\x_{2}=-2\\\\Otvet:\boxed{-2;2}\\\\\\4)x^{2}+20x+91=0\\\\D=20^{2}-4*91=400-364=36=6^{2}\\\\x_{1}=\frac{-20+6}{2}=-7\\\\x_{2}=\frac{-20-6}{2}=-13\\\\Otvet:\boxed{-7;-13}$