How do you graph #y = 2x^ 2-13x-7#?

1 Answer
Feb 20, 2018

See below for a full explanation:

Explanation:

You can find the #"zeroes (x-intercepts), y-intercepts, and the vertex."#

The standard form of a quadratic equation is

#ax^2+bx+c#

with #c# being the #"y-intercept"#.

The #"y-intercept"# of this equation is #-7# as #c# is #-7#.

To find the #"zeroes"#, plug #0# for #y#. Use the quadratic formula.

#(-b+-sqrt(b^2-4ac))/(2a)#

Identify #a,b,"and"# #c#:

#a=2#

#b=-13#

#c=-7#

Plug in:

#(-(-13)+-sqrt((-13)^2-4*2*-7))/(2*2)=>#

#(13+-sqrt(225))/4=>#

#(13+-15)/4#

The zeroes are

#7,-1/2#

This was also factorable, as a discriminant (#b^2-4ac#) that is a perfect square tells us that the equation is factorable (#225# is a perfect square).

You could factor and get

#(2x+1)(x-7)=>#

#x=7,-1/2#

To get the vertex of an equation #ax^2+bx+c#, use:

#h=(-b)/(2a)#

#k=c-(b^2)/4a#

with #(h,k)# being the vertex:

#a=2#

#b=-13#

#c=-7#

#h=(-(-13))/(2*2)=>13/4#

#k=-7-((-13)^2)/(4*2)=>-56/8-169/8=>-225/8#

The vertex is #(13/4,-225/8)#

#----------------#

Summary:

#"y-intercept":(0,7)#

#"x-intercepts": (7,0) and# #(-1/2,0)#

#"vertex":(13/4,-225/8)#