How do you find the vertex and the intercepts for #y=2x^2-12x#?

1 Answer
Apr 27, 2016

#color(blue)( y_("intercept")" is at y=0")#

#color(blue)(x_("intercepts")-> x=0; x=4)#

#color(blue)("Vertex"->(x,y)=(3,-18))" "->" and is a minimum"#

Explanation:

Write as:#" "y=2x^2-12x +0#

#color(blue)("The y intercept is at y=0")#

y =0 at x=0

#color(brown)("so one of the x intercepts is at x=0")#
'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
write as #y=2(x^2-6x)#

#color(blue)(x_("vertex") = (-1/2)xx(-6) = +3)#

#color(brown)(y=2x^2-12xcolor(green)(" "->" "y_("vertex")=2(3)^2-12(3) =-18))#

#color(blue)(y_("vertex")=-18)#

#color(blue)("Vertex"->(x,y)=(3,-18))#

#color(brown)("As the coefficient of "x^2" is positive then the general shape of")##color(brown)("the graph is " uu)# #color(blue)(" Thus the vertex is a Minimum")#
'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

#x_("intercpt")->y=0#

# => 0=2(x^2-6x)#

Divide both sides by 2

#=>0/2=2/2(x^2-6x)#

But #0/2=0" and "2/2=1#

#=>0=(x^2-6x)#

Factor out #x#

#=>0=x(x-4)#

For #y=0 ; x=0" and/or "x=+4#

#color(blue)(x_("intercepts")-> x=0; x=4)#
'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~