Posted by tammi on Monday, October 7, 2013 at 6:03pm.
can someone show me how to solve this the instructions are for me to solve by the quadriatic formula is this really 8 grade math im confused im trying to help my daughter tammi and i have never run across this before
X^2 + 9=0

algebra  Reiny, Monday, October 7, 2013 at 6:56pm
If the instructions are to solve by the quadratic formula, then this topic could be in grade 8 depending in what country you live.
for any equation of the form
ax^2 + bx + c = 0,
x = (b ± √(b^24ac) )/(2a)
for your x^2 +9 = 0
a = 1, b = 0 , and c = 9
x = (0 ± √(036)/2
= ± √36/2
= 3i , where i = √1 , if she has studied complex numbers
or
there is no solution in the set of real numbers since we cannot take the square root of a negative number
could be done without the formula.....
x^2 + 9 = 0
x^2 = 9
x = ± √9 = ± 3i as before
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