Exam 2, Question 7 – root of an equation

[Jeffrey Chudy]

Exam 2, Question 7 – root of an equation

[Anonymous]

Question 7 : Determine the roots of the equation 2x^2 + 3x – 5 = 0
(a) -2.5, -1
(b) 0, 0
(c) -1, 2.5
(d) -2.5, 1

What is the fastest way to solve?
I quickly realized that I need a positive and negative # need to be multiplied to get a -5. This eliminated 2 answers (a + b). Next I plugged in -1 which didnt solve the equation. +1 did solve the equation, narrowing it down to answer (d).

[Anonymous]

The fastest way to solve is to recognise that the expression 2x^2+3x-5 factorises as (2x+5)(x-1).
So this means that (2x+5)(x-1) = 0 ==> 2x+5 = 0, which gives the root x = -2.5, or x-1 = 0, which gives the root x=1

[Author]

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