Question

How do you solve `x^2+3x-70=0` by completing the square?

Answer 1

When the `x`-coefficient (in this case `3`) is odd, completing the square is not the best method.

Explanation:

Consider the sum-product-method instead: The task is to factor `-70` into two factors that add up to `3`.

After some trying you may find that `10and-7` will do the job.
Now you can factorise the left part of the equation:

`->(x+10)*(x-7)=0` so either:
`x+10=0->x=-10orx-7=0->x=7`