Question

B= ? a= 20 m= 5
b²= a•m ​

Answer 1

$a = 20, m = 5\\\\b^2 = 20 \cdot 5\\b^2 = 100\\\sqrt{b^2} = \sqrt{100}\\\boldsymbol{b = \pm 10}$

Answer 2

Olá!

DADOS:

b = ?

a = 20

m = 5

$b^{2} = a \cdot m\\ \\ b^{2} = 20 \cdot 5\\ \\ b^{2} = 100 \\ \\ \sqrt{b^{2}}~=~\sqrt{100} \\ \\ \\ \boxed{b=10}$

:)