Question 246169
sqrt( x + 5) = sqrt(x^2 - 15)
square both sides
x+5=x^2-15
subtract x+5
0=x^2-x-10

*[invoke quadratic "x", 1, -1, -10 ]
we can also solve by completing the square
add 10 to both sides
10=x^2-x
add (1/2)^2 to both sides
41/4=x^2-x+1/4
factor
41/4=(x-1/2)^2
get sqrt
sqrt(41)/2=x-1/2
-sqrt(41)/2=x-1/2
add 1/2 to both sides
1/2-sqrt(41)/2=x
1/2+sqrt(41)/2=x
factor
1/2(1-sqrt(41))=x

1/2(1+sqrt(41))=x