2x^2-x-2020=0
=>x=(1+căn 16161)/4 hoặc x=(1-căn 16161)/4
Gọi A(1+căn 16161/4;0); B(1-căn 16161/4;0); N(0;b)
\(AB=\dfrac{\sqrt{2\cdot\sqrt{16161}}}{2};AN=\sqrt{\left(0-\dfrac{1+\sqrt{16161}}{4}\right)^2+\left(b-0\right)^2}\)
\(BN=\sqrt{\left(0-\dfrac{1-\sqrt{16161}}{4}\right)^2+\left(b-0\right)^2}\)
ΔABN vuông tại N
=>NA^2+NB^2=AB^2
=>\(\left(\dfrac{1+\sqrt{16161}}{4}\right)^2+b^2+\left(\dfrac{1-\sqrt{16161}}{4}\right)^2+b^2=\left(\dfrac{1+\sqrt{16161}}{4}-\dfrac{1-\sqrt{16161}}{4}\right)^2\)
=>b^2=-2(1-16161)/16*2=1010
=>b=căn 1010
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