SOLUTION: f(x)= 72x^2+ 13x-15 how do i graph this function by hand and find the x and y interceptsand the vertex as well as any other points plotted

Algebra ->  Graphs -> SOLUTION: f(x)= 72x^2+ 13x-15 how do i graph this function by hand and find the x and y interceptsand the vertex as well as any other points plotted      Log On


   

Question 70792: f(x)= 72x^2+ 13x-15 how do i graph this function by hand and find the x and y interceptsand the vertex as well as any other points plotted
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Pick some x-values that will help you. The best ones are
x = 0
x = +1
x = -1
Then compute the y-value that goes with each x-value
In this case,
x = 0, y = -15
x = +1, y = 70
x = -1, y = 44
The y-intercept is -15 as you can see
To find the x-intercept, make y=0 and find x
with the quadratic formula
x+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+
this gives you 2 values for x because of the +/- in front
of the square root
Your equation is in the form y+=+ax%5E2+%2B+bx+%2B+c
a = 72
b = 13
c = -15
The vertex will be the value which is exactly between
the the x-values that make y=0, and that is -b%2F2a