Question 989426
{{{5x^2 + 35 =0}}}
5 is a factor and lets ignore it.

{{{5(x^2+7)=0}}}
{{{x^2+7 =0}}}
{{{x^2 = -7}}}

you have learnt that {{{i^2 = -1}}}

{{{x^2 = 7i^2}}}

{{{x}}} equals plus or minus {{{sqrt(7)*i}}}