Question 14007
What you are doing wrong is distributing the two before taking the square. In equations certain operations have higher "authority" to perform before the others.  Just remember the work PEMDAS. It means Parentheses Exponents Multiplication Division Addition Subtraction. These operations have "authority" going from highest to lowest, that is, Parentheses is the highest authority and Subtraction is the lowest.
 Try this:
{{{2*(5x+3)^2}}}=38
2({{{25x^2 + 30x + 9}}}) = 38.
NOW distribute the 2:
{{{50x^2}}} + 60x + 9 = 38.
subtract 38 from both sides.
{{{50x^2}}} + 60x - 29 = 0.
Now use the quadratic formula to solve for x.
x = {{{(-60+-sqrt(60^2-4*50*(-29)))/(2*50)}}}.

See if this works.