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

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Discussion Overview

The discussion revolves around solving a system of equations representing a straight line and a quadratic curve. Participants explore the intersection points of the equations and express confusion regarding discrepancies between their calculations and textbook answers.

Discussion Character

  • Homework-related

Main Points Raised

  • One participant presents the equations y=3x+11 and y=2x²+2x+5, stating they found the intersection points to be (-2,5) and (2.5,18.5).
  • The participant claims to have factorized the resulting quadratic equation correctly as (2x+4)(x-2.5) and checks their work by expanding it back.
  • Another participant questions the arithmetic of multiplying 4 by 2.5, suggesting a potential error in calculations.
  • Further replies clarify that 4 multiplied by -2.5 equals -10, indicating a misunderstanding in the original participant's calculations.
  • The original poster expresses frustration and embarrassment over their arithmetic mistake, questioning their capability in mathematics.

Areas of Agreement / Disagreement

Participants generally agree that there is a calculation error in the original post, but the discussion does not resolve the discrepancy between the calculated intersection points and those provided by the textbook.

Contextual Notes

The discussion highlights potential misunderstandings in arithmetic operations and their impact on solving quadratic equations, but does not address the underlying assumptions or definitions used in the problem.

bob4000
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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
 
Mathematics news on Phys.org
Is 4*2.5=6?
 
its 4*-2.5=-6
 
Remarkable. My calculator says that 4* -2.5= -10.

4*(2- .5)= 6
 
4*(-2.5)=-10
 
omg! i feel so goddamn stupid! :blushing:

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

thnx again.
 

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