Question 49165
You can not take a square root of a negative number, so you can only take the square root of a positive number or the value of zero.
{{{3x + 21 >= 0}}}
{{{3x >= -21}}}
{{{x >= -7}}} (a.)
{{{graph(600,600,-10,10,-10,10,7+sqrt(3x+21))}}}