Question

3 ( x ao quadrado - 18 ) = 21

Answer 1

$3( {x}^{2} - 18) = 21$

$3 {x}^{2} - 54 = 21$

$3 {x}^{2} = 21 + 54$

$3 {x}^{2} = 75$

$x {}^{2} = \frac{75}{3}$

${x}^{2} = 25$

$x = \sqrt{25}$

$x = 5$