Answer:
A student is incorrect, he should add 16, not 64.
Step-by-step explanation:
Given the equation [tex]- 23 = x^2 + 8x[/tex]
To use formula
[tex](a+b)^2=a^2+2ab+b^2,[/tex]
note that
[tex]8x=2\cdot x\cdot 4,[/tex]
so we need to add [tex]4^2=16[/tex] to complete the square
Therefore,
[tex]-23+16=x^2+8x+16\\ \\-7=(x+4)^2[/tex]
A student is incorrect, he should add 16, not 64.