$\operatorname{log}\left(x\right) + \operatorname{log}\left(x + 21\right) = 2$

$2\operatorname{log}_{4}\left(x\right) − \operatorname{log}_{4}\left(3\right) = 2$

$\operatorname{log}_{2}\left(9x + 5\right) − \operatorname{log}_{2}\left(x^{2} − 1\right) = 2$

$\operatorname{log}_{7}\left(x + 1\right) + \operatorname{log}_{7}\left(x − 5\right) = 1$