If x^2 - 1 = 0 and x > 0, which of the following must be equal to 0 ?	Choose the correct option
A) x^2 - 9x B) x^2 - 9x + 20 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 +2x-3 = 1+2-3  2 +2 -3= 
<gadget id="calculator"> 2 +2 -3</gadget>
<output>1</output>
1+2-3= 
<gadget id="calculator">1+2-3</gadget>
<output>0</output>
0   x^2 + 2x - 3 is also the answer
<result>D</result>
If x^2 - 1 = 0 and x > 0, which of the following must be equal to 0 ?