Question

Известно что √(13+z^3)+√(z^3-14)=3 найти √(13+z^3)-√(z^3-14). Как это решить

Answer 1

Ответ.

$\sqrt{13+z^3}+\sqrt{z^3-14}=3\\\\(\sqrt{13+z^3}+\sqrt{z^3-14})\cdot (\sqrt{13+z^3}-\sqrt{z^3-14})=\\\\=(\sqrt{13+z^3})^2-(\sqrt{z^3-14})^2=(13+z^3)-(z^3-14)=13+14=27\\\\\\\sqrt{13+z^3}-\sqrt{z^3-14}=\dfrac{27}{\sqrt{13+z^3}+\sqrt{z^3-14}}\\\\\\\sqrt{13+z^3}-\sqrt{z^3-14}=\dfrac{27}{3}\\\\\\\sqrt{13+z^3}-\sqrt{z^3-14}=9$

$\star \ \ \ (a+b)(a-b)=a^2-b^2\ \ \star$