[tex]\qquad \qquad\huge \underline{\boxed{\sf ᴀɴsweʀ}}[/tex]
Let's solve ~
[tex]\qquad \sf \dashrightarrow \: {x}^{2} - 21 = 79[/tex]
[tex]\qquad \sf \dashrightarrow \: {x}^{2} = 79 + 21[/tex]
[tex]\qquad \sf \dashrightarrow \: x {}^{2} = 100 [/tex]
[tex]\qquad \sf \dashrightarrow \: x = \pm\sqrt{100} [/tex]
[tex]\qquad \sf \dashrightarrow \: x = \pm \sqrt{10 \times 10} [/tex]
[tex]\qquad \sf \dashrightarrow \: x = \pm10[/tex]
