$x²+7x+16=0$
$↔x²+2.\dfrac{7}{2}.x+\dfrac{49}{4}+\dfrac{15}{4}=0$
$↔\bigg(x+\dfrac{7}{2}\bigg)²+\dfrac{15}{4}=0$
Vì $\bigg(x+\dfrac{7}{2}\bigg)²≥0$
$→\bigg(x+\dfrac{7}{2}\bigg)²+\dfrac{15}{4}>0∀x$
$→$ Pt đã cho vô nghiệm
Vậy pt đã cho vô nghiệm $x∈\{\varnothing\}$