Question

Solve the quadratic equation by completing the square.
x^2+18x+70=0

Answer 1

hint:
we can write:
\[\large {x^2} + 18x + 70 = {x^2} + 18x + 81 - 81 + 70 = ...?\]

Answer 2

I'm confused...

Answer 3

note that x^2 + 18x + 81 can be written as a perfect square

Answer 4

that's right! @welshfella

Answer 5

Is it like this format: (?)
(x+ _ )^2 = _
(x- _ )^2 = -

Answer 6

\[\large {x^2} + 18x + 81 - 81 + 70 = \left( {{x^2} + 18x + 81} \right) - 81 + 70 = ...?\]

Answer 7

hint:
what is (x+9)^2=...?

Answer 8

yes

Answer 9

notice that 81 is a perfect square

Answer 10

Would it be (x+9)^2=9 ?

Answer 11

NO wait so x would be 9!

Answer 12

after that computation, you should get this:
\[\large \left( {{x^2} + 18x + 81} \right) - 81 + 70 = {\left( {x + 9} \right)^2} - 11\]

Answer 13

I'm still confused