Answer:
b=12 or b=-12
Step-by-step explanation:
If the quadratic equation [tex]2x^2+bx+18=0[/tex] has a double root, then its discriminant is equal to zero. Find the discriminant:
[tex]D=b^2-4\cdot 2\cdot 18=b^2-144.[/tex]
Now equate the discriminant to 0:
[tex]b^2-144=0,\\ \\b^2=144,\\ \\b=\pm 12.[/tex]
