Question

kak tyt x²-x-20=0 polychilos

Answer 1

$\sqrt{x^{2} +x-21}=\sqrt{2x-1} \\\\ODZ:\\\\\left \{ {{x^{2}+x-21\geq0 } \atop {2x-1\geq 0}} \right. \\\\\Big(\sqrt{x^{2} +x-21}\Big)^{2} =\Big(\sqrt{2x-1}\Big)^{2}\\\\x^{2} +x-21=2x-1\\\\x^{2} +x-21-2x+1=0\\\\x^{2} -x-20=0\\\\D=(-1)^{2}-4\cdot(-20)=1+80=81=9^{2} \\\\x_{1} =\dfrac{1+9}{2} =5\\\\x_{2} =\dfrac{1-9}{2} =-4-neyd \ , \ tak \ kak \ 2x-1\geq0 \ , \ 2\cdot (-4)-1=-9<0\\\\Otvet:\boxed5$