Answer:
[tex](x+5)^2=4[/tex]
Step-by-step explanation:
We have:
[tex]x^2+10x+21=0[/tex]
First, subtract 21 from both sides:
[tex]x^2+10x=-21[/tex]
Now, we can complete the square. We will divide the coefficient of the b term and square it. So:
[tex](\frac{b}{2})^2\Rightarrow(\frac{10}{2})^2=(5)^2=25[/tex]
So, we will add 25 to both sides:
[tex](x^2+10+25)=-21+25[/tex]
The left is the perfect square trinomial pattern. Add on the right:
[tex]((x)^2+2(5)(x)+(5)^2)=4[/tex]
Final step:
[tex](x+5)^2=4[/tex]
