Question

Solve x2 + 18x – 19 = 0 by completing the square.

Answer 1

Answer:

x = 1, x = -19

Step-by-step explanation:

1) factorise

(x−1)(x+19)=0

2) equal to 0

x−1=0 or x+19=0

x=1 or x=−19

Answer 2

Answer:

$x = 1$

$x = 19$

Step-by-step explanation:

Set up equation

${x}^{2} + 18x - 19 = 0$

Add 19 on both sides

${x}^{2} + 18x = 19$

Divide 18 by 2 and sqr it.

$( \frac{18}{2}) {}^{2}$

${9}^{2} = 81$

Add 81 on both sides

${x}^{2} + 18x + 81 = 100$

Using the AC method, isolate the left side into a binomial.

$(x + a)(x + b)$

that a and b can be added to equal 18 and be multiplied to equal 81.

Only number that does that is 9. 9+9=18, 9×9=81

$(x + 9)(x + 9)$

$(x + 9) {}^{2}$

Set up equation

$(x + 9) {}^{2} = 100$

Take sqr root of both sides

$x + 9 = 10$

Since sqr root of a positve number can be negative, set up this equation also

$x - 9 = 10$

$x = 1$

OR

$x = 19$