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

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Answer 1 · 2015-07-06T10:47:33

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

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:
$x+10=0->x=-10orx-7=0->x=7$

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