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^2-4ac) )/(2a)

for your x^2 +9 = 0

a = 1, b = 0 , and c = 9

x = (0 ± √(0-36)/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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