If x^2 - 1 = 0 and x > 0, which of the following must be equal to 0 ?	Choose the correct choice from the following choices:
A) x^2 - 9x
B) x^2 - 9x + 8
C) x^2 - 2x + 3
D) x^2 + 2x - 3
E) x^2 + 5x + 6
x^2-1 = 0   x= +1 or x = -1   if we substitute x= 1 in the equation x^2 -9x+8 = 1-9+8  2 -9 +8= 
<gadget id="calculator"> 2 -9 +8</gadget>
<output>1</output>
1-9+8= 
<gadget id="calculator">1-9+8</gadget>
<output>0</output>
0   x^2 - 9x + 8 is also the answer
<result>B</result>
If x^2 - 1 = 0 and x > 0, which of the following must be equal to 0 ?