Question

Solve x2 + 8x − 3 = 0 using the completing-the-square method.

A.x = four plus or minus the square root of three
B.x = negative four plus or minus the square root of three
C.x = four plus or minus the square root of nineteen
D.x = negative four plus or minus the square root of nineteen

Answer 1

(x + 4)^2 - 16 - 3 = 0

can you see why i subtract 16 ?

Answer 2

nope lol

Answer 3

ok so to complete the square you first divide the coefficient of x in the original equation by 2

so here its +8 / 2 = +4

so we write (x + 4)^2 - thats the square bit

but if you expand this it comes to x^2 + 8x + 16. So to make it equal to x^2 + 8x we have to subtract 16

Answer 4

okay i dont undertand how there is a squaare root in the answer tho

Answer 5

as an identity in general form its is

x^2 + bx = (x + (b/2)^2 - ( b/2)^2

Answer 6

because we have a square in the equation

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

taking square roots

x + 4 = +/- sqrt 19

Answer 7

x = -4 +/- sqrt 19