Use formula and complete the square explain/show?

Question

Even using the formula I can't even get the right anwser this is none sense.
-b+/-√b²-4ac /2a

Prob.
-x²-8x+3=0

Solving.
x²+8x-3=0
-8+/-√64-4*1*-3/2

x=-8+/-√76/2

The anwser is totally wrong, how useless the formula is...

Complete the square.

(x+8/2)²-64/4=-3 +64/4
(x+8/2)²=52/4
(x+8/2)=2+/-√13/2
X=-8+/-√13/2

Answer 1

You're missing parentheses, it's:

(-b+/-√(b² - 4ac)) / 2a

The "-b" part is divided by "2a" as well, so instead of -8, it should be -4.

For your equation, after multiplying by -1 so that the coefficient of x^2 is positive: a = 1, b= 8, c=-3

x = {-(8) +/- √[(8)^2 - 4*1*(-3)]}/2*(1)
x = { -8 +/- √[64 + 12] } / 2
x = -4 +/- √(76)/2
x = -4 +/- √(19)

Since √(76)/2 = √(4*19)/2 = 2√(19)/2 = √(19)

====================

Completing the square:

x^2 + 8x - 3 = 0
x^2 + 8x = 3
x^2 + 8x + (8/2)^2 = 3 + (8/2)^2
(x + 8/2)^2 = 3 + 4^2
(x + 4)^2 = 3 + 16
(x + 4)^2 = 19
x + 4 = +/- √(19)
x = -4 +/- √(19)

I get the same answer either way.

Answer 2

Your final equation for the two roots should look as follows:
(8 +/-(76)^1/2))/(-2) note the entire upper part, as a final solution, is divided by the 2a value OR-- 8/2 +/-(76^1/2)/2 hope this helps!

Answer 3

Formula says
x = (-8 +/- sqrt( 64 - (4)(1)(-3)) ) / 2
= (-8 +/- sqrt( 76) ) / 2
= (-8 +/- sqrt( (4)(19))) / 2
= -4 + sqrt(19) or -4 - sqrt(19)

(EDITED: Had math error)

Answer 4

-x^2-8x+3=0
x^2+8x-3=0
x^2+8x=3
(x)^2+2*x*4+(4)^2=3+16 [adding (4)^2 or 16 to both sides]
(x+4)^2=19
x+4=+-sqrt 19
x= -4+-sqrt 19 ans