Answer:
b = -1
Step-by-step explanation:
First plug in 4 for each x:
[tex]x^2+bx-12=0\\(4)^2+b(4)-12=0[/tex]
Then simplify by multiplying out what you can with 4:
[tex](4)^2+b(4)-12=0\\16+4b-12=0[/tex]
After simplify further by combining like terms:
[tex]16+4b-12=0\\4b +4=0[/tex]
Then isolate b on one side by subtracting 4 from each side:
[tex]4b+4=0\\(-4)+4b+4=0+(-4)\\4b=-4[/tex]
Finally isolate b further by dividing each side by 4 to get b alone and find the answer:
[tex]4b=-4\\\frac{4b}{4}=\frac{-4}{4} \\ b=-1[/tex]
