Question

x^2+7=8x
x^2+18=9x
(-2x+1)(-2x-7)

Answer 1

$1)\; \; x^2+7=8x\; \; \to \; \; x^2-8x+7=0\; ,\\\\x_1=1\; ,\; x_2=7\; (teodrema\; Vieta)\\\\2)\; \; x^2+18=9x\; \; \to \; \; x^2-9x+18=0\; ,\\\\x_1=3\; ,\; x_2=6\; \; (teorema\; Vieta)\\\\3)\; \; (-2x+1)(-2x-7)=0\\\\4x^2+14x-2x-7=0\; \; \to \; \; 4x^2+12x-7=0\\\\D/4=6^2+4\cdot 7=64\; ,\; \; x_1=\frac{-6-8}{4}=-3,5\; ;\; \; x_2=\frac{-6+8}{4}=0,5$