SOLUTION: x^2-5x-7<0 Help! :)

Algebra ->  Quadratic Equations and Parabolas  -> Quadratic Equations Lessons  -> Quadratic Equation Lesson -> SOLUTION: x^2-5x-7<0 Help! :)      Log On


   

Question 1923: x^2-5x-7<0
Help!
:)
Answer by longjonsilver(2297) About Me  (Show Source):
You can put this solution on YOUR website!
easy...do not be scared of inequalities.
Solve x%5E2-5x-7=0
You cannot factorise this, so use the formula..see my recent answers on this method.
Answers here are x+=+%285%2Bsqrt%2853%29%29%2F%282%29 and x+=+%285-sqrt%2853%29%29%2F%282%29. These are called the roots of the equation. Note the "5+" answer is a bigger number than the "5-" number.
Now, any +x^2 graph is u-shaped and I have just found where it crosses the x-axis, so where will the curve have negative values? Well, any x value between these 2 root values (just sketch a u-shaped curve that cuts the x-axis to see what i mean, so this is your inequality answer.
%285-sqrt%2853%29%29%2F%282%29 < x < %285%2Bsqrt%2853%29%29%2F%282%29
Hope this makes sense.
cheers
Jon.