Respuesta :

Answer:

a. -2x^2 + 3x+5=y

b.-x^2 +5x-4=y

c.-x^2 +6x-12=y

Step-by-step explanation:

a.y=-2x^2 +bx+c

the points P and Q lie on curve

[tex]\left \{ {{-b+c=2} \atop {b+c=8}} \right.[/tex]

=> b=3, c=5

b. delta = b^2 +4c

x1= [tex]\frac{-b+\sqrt{b^{2}+4c } }{-2}[/tex] =4

=> [tex]b-\sqrt{4c+b^{2} }[/tex]=8

x2=[tex]\frac{-b-\sqrt{b^{2}+4c } }{-2}[/tex]=1

=>2=b+[tex]\sqrt{b^{2}+4c }[/tex]

suppose : [tex]\sqrt{b^{2}+4c }[/tex] = a

=> [tex]\left \{ {{a+b=2} \atop {-a+b=8}} \right.[/tex]

=> a=-3

b=5

a=-3 =>  [tex]\sqrt{b^{2}+4c }[/tex] =-3 => b^2 +4c =9 =>5^2 +4c=9 => c=-4.

c.vertex (3;-3)

[tex]\frac{-b}{-2}[/tex]=3 => b =6

[tex]\frac{-D}{4a}[/tex]=[tex]\frac{-b^{2}+4ac}{-4}[/tex] =-3 =>-b^2+4ac=12 => c=-12.