Question

sabendo que a2+4b2 = 116 e (a-2b)2 = 36, qual o valor de ab ?

Answer 1

vamos lá...

$Se~~a^2+4b^2=116~~~e~~~~(a-2b)^2=36$

para calcular ab vamos resolver

$(a-2b)^2=36 \\ a^2-4ab+4b^2=36 \\ \\ (a^2+4b^2)-4ab=36 \\ \\ 116-4ab=36 \\ -4ab=36-116 \\ -4ab=-80~~\times(-1) \\ \\ 4ab=80 \\ ab=80\div4 \\ ab=20$