Solving Quadratic Equations: (-2,5), (2.5,18.5) Answers Explained

[bob4000]

hey there reader

i have:
y=3x+11
y=2xsquared+2x+5

i have to solve these as they are represent a straight line and a curve respectively. so far i have:

3x+11=2xsquared+2x+5 at the intersection

;2xsquared-x-6=0

i factorised this and checked it to make sure it matched the above equation:

(2x+4)(x-2.5)

when i multiplied it out to check it i got: 2xsquared-x-6=0, which is alrite

when going on to solve x and y, i end up with:

x=-2
x=2.5
putting these into y=3x+11 i got:

y=5
y=18.5

finally giving the intersections of (-2,5) and (2.5,18.5)

however the answers given by the textbook from which the question was taken from, the intersections are (-1.5,6.5) and (2,17)

im really confused and would be much obliged for any help given

thank you

 

[arildno]

Is 4*2.5=6?

 

[bob4000]

its 4*-2.5=-6

 

[HallsofIvy]

Remarkable. My calculator says that 4* -2.5= -10.

4*(2- .5)= 6

 

[arildno]

4*(-2.5)=-10

 

[bob4000]

omg! i feel so goddamn stupid!

thnx guys. i don't think i should be doing as level maths if i can't do 4*-2.5!

thnx again.