Question Number 171823 by Mikenice last updated on 21/Jun/22
$${solve}\:{for}\:{y}: \\ $$$${y}^{\mathrm{4}} −\mathrm{34}{y}^{\mathrm{2}} +\mathrm{225}=\mathrm{0} \\ $$
Answered by nimnim last updated on 21/Jun/22
$$\left({y}^{\mathrm{2}} −\mathrm{9}\right)\left({y}^{\mathrm{2}} −\mathrm{25}\right)=\mathrm{0} \\ $$$${either}\:\:{y}^{\mathrm{2}} −\mathrm{9}=\mathrm{0}\:\:{or}\:\:\:{y}^{\mathrm{2}} −\mathrm{25}=\mathrm{0} \\ $$$$\:\:\:\:\:\Rightarrow\:{y}=\pm\mathrm{3}\:\:{or}\:\:\:{y}=\pm\mathrm{5}= \\ $$