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

1 Answer
Jul 6, 2015

Answer:

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#