Question

a) 7x² - 21 = 0
b) x² + 9 = 0
c) x² - 49 = 0
d) 5x² - 20 = 0 
Me ajuda ai gente . Como faz essas contas ?

Answer 1

a) 7x² - 21 = 0
x(7x - 21) = 0 → x= 0 1° raiz | 2° raiz 7x - 21= 0
x = 21/7 = 3
b) x² + 9 = 0 → x(x + 9) = 0 → 1° raiz x= 0 | 2° raiz
x = -9
c) x² - 49 = 0 → x(x - 49) = 0 → 1° raiz x= 0
2° raiz x - 49 = o → x = 49

Answer 2

$a)7x^{2}-21=0 =>7x^{2}=21 => x^{2}= \frac{21}{7}=x^{2}=3 => \sqrt{3}\\S=[+ \sqrt{3},-\sqrt{3} ]\\\\b)x^{2}+9=0 =>x^{2}=-9=>x= -\sqrt{9}=-3\\\\c)x^{2}-49=0 =>x^{2}=49=>x= \sqrt{49}=7\\\\d)5x^{2}-20=0=>5x^{2}=20=>x^{2}= \frac{20}{5}=>x^{2}=4 => x= \sqrt{4}=2 :.$