` a) ` ` \sqrt{x - 2020} = \sqrt{2019 - 1} `
` => x - 2020 = 2018 `
` => x = 4038 `
` b) ` ` \sqrt{4x^{2}-12+9}=2020 `
` => \sqrt{4x^2 - 3} = 2020 `
` => 4x^2 - 3 = 2020^2 `
` => 4x^2 = 2020^2 + 3 `
` => x^2 = \frac{2020^2}{4} + 3/4 `
` => x^2 = 505.2020 + 3/4 `
` => x^2 = 1020100 + 3/4 `
` => x^2 = \frac{4080403}{4} `
` => ` \(\left[ \begin{array}{l}x=\frac{\sqrt{4080403}}{2}\\x=-\frac{\sqrt{4080403}}{2}\end{array} \right.\)