So far we have considered quadratic expressions with no x1 term. In this video we show how to handle expressions like √x2+4x−5 or x2+2x+5.
The key is the identity
(x+b2)2=x2+bx+b24
This means that any quadratic polynomial x2+bx+c can be converted to a sum or difference of squares:x2+bx+c=(x+b2)2+(c−b24)=(x+b2)2±a2,
depending on whether c−b2/4 is positive or negative (we have set |c−b2/4|=a2). We then use our usual trig substitutions by setting x+b2=atan(θ), or asin(θ), or asec(θ).
In the video, we apply this technique to three examples.