Hi, I'm new to Math Help Forum and was wondering if you could help me with functions and finding the x-intercepts and the coordinates of the vertex.
I'm having a hard time with these questions:
y=x^2+7x
and
y= 15x^2+16-7
Can you please explain step by step. I use the quadratic formula but my anwser seems be be wrong.
thanks for taking time to read this, hopefully you can help.
Since you going to have to complete the square to find the vertex anyway, I would prefer using that to find the y- intercepts rather than the quadratic formula.
Half of 7 is 7/2 and the square of that is 49/4:
At this point you can argue that is never negative so y is always "plus something". That tells you than the lowest value for y is which occurs when or .
The vertex is at
Now, going back to ,
adding to each side gives
and so
so that
or .
Of course, for this problem, the simplest way to do it is to factor:
so either x= 0 or x+ 7= 0 and x= -7.