Posted by Allison A on .
Solve by completing the square
x^2+4x21=0
Help how do I do this???

Math 
Fizzylicous,
For this go on to the website discovery education. Then go under students and click math. And then where it says step by step math in green, click on trigonmetry and calculus. I forgot what area of math this is but choose from one of the items. And jot it in the box search thing and when you press enter it gives you the answer with a wonderful explanation on how to get there. I've used it for math a couple of times.

Math 
Reiny,
x^2+4x21=0
x^2+4x = 21
take half the middle term coefficient, square it, then add it to both sides
x^2 + 4x + 4 = 21 + 4
(x+2)^2 = 25
x+2 = ± √25 = ± 5
x = 2 ± 5
x = 3 or 7