Solve the given equation

$3.2{\mathrm{cos}}^{2}\theta +\mathrm{sin}\theta =1\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}4.{\mathrm{sin}}^{2}\theta =4-2{\mathrm{cos}}^{2}\theta$

$5.{\mathrm{tan}}^{2}\theta -2\mathrm{sec}\theta =2\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}6.{\mathrm{csc}}^{2}\theta =\mathrm{cot}\theta +3$