How do you solve #0.9x - 0.7x^2 = -1 # using the quadratic formula?

Question

1868 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2017-04-04T00:38:37

I got: #-5/7 and 2#

We can first multiply by #10# and write it in the form: #ax^2+bx+c=0#:

so:
#10*(0.9x-0.7x^2)=10*(-1)#

#9x-7x^2=-10#

#-7x^2+9x+10=0#

#x_(1,2)=(-9+-sqrt(81-4(-7*10)))/-14=(-9+-sqrt(361))/-14=(-9+-19)/-14#

#x_1=(-9+19)/-14=-10/14=-5/7#
#x_2=(-9-19)/-14=28/14=2#