EXPLANATION
The third needed term would be the following:
Dividing both sides by 4:
[tex]x^2+\frac{3}{4}x=0[/tex]Multiplying the second term by 1/2 and the squared power:
[tex](\frac{1}{2}*\frac{3}{4})^2=\frac{9}{64}[/tex]Adding 9/64 to both sides:
[tex]x^2+\frac{3}{4}x+\frac{9}{64}=\frac{9}{64}[/tex]Finally, we can conclude the third term is 9/64.