Mathieu is finding the x-intercepts of the function f(x) = x2 + 4x + 3. his work is shown below . which error did mathieu make?

I can't see Mathieu's work but I will show the right steps and maybe you can find where Mathieu went wrong.

f(x)=x^2+4x+3

f(x)=(x+3)(x+1)       Since 3*1=3 and 3+1=4

The x-intercepts can be found by setting y to 0 and solving for x

(in other words replace that f(x) thing with 0 and solve for x)

0=(x+3)(x+1)

Now set both factors equal to 0

x+3=0       or      x+1=0

x   =-3                    x=-1

The x-intercepts are at (-3,0) and (-1,0)