Solving quadratic eqn 2x^2 + x - 1 = 0 w/ Quad. Formula

[rage]

Can someone tell me if this is correct?

2x^2 + x - 1 = 0
ax^2 + bx + c = 0
a=2, b=1, c=-1

x = -b +- square root(b^2 - 4ac)/2a
= -1 +- square root(1^2 - 4(2)(-1)
= -1 +- square root(9)/2*2
= -1 +- square root(9)/4

I am pretty sure I did this correct; however, since the square root of 9 is 3 would the answer be
= -1 +- 3/4
or would it be =-1 +- square root(3)/4

 

[galactus]

Plug them back into your quadratic. Do you get 0?. If not, then try again.

 

[Denis]

or would it be =-1 +- square root(3)/4

Not quite; it's sqrt(9), AND with add'l brackets: x = [-1 +- sqrt(9)] / 4
so x = (-1 + 3) / 4 or x = (-1 - 3) / 4

To make sure you're right, simply substitute x values back in original equation.