#### Answer

$x=(−5,-3)$

#### Work Step by Step

Step -1 : Add the square of half of the co-efficient of $x$ to both sides.
Co-efficient of $x = 8$
Half of $8 = \frac{1}{2}×8=4$
Square of $4$ is $4×4=16$
The equation becomes $x^2+8x+16=-15+16$
Step-2 Factor the trinomial and simplify the right hand side.
$(x+4)^2=1$
Step-3 Use the square root property and solve for $x$
$(x+4)=±\sqrt 1$
$x+4=±1$
Step-4 Subtract 4 on both the sides
$x=−4±1$
Therefore the solution set is $(-5,-3)$