Solved Example

+2 votes
Solve for x: 2x^2 - 11x - 21 = 0
asked Jun 24, 2013 in Algebra by answermachine ~Rookie~ (120 points)
    

2 Answers

0 votes
Solution: 2x^2-11x-21=0
 

a=2,b=-11,c=-21
 

x=-b±√b^2-4ac/2a
x=11±√(-11)^2-4*2*(-21)/2*2

 

x=5.99035,
x=0.49035

answered Aug 13, 2013 by Jonasmathwork ~Rookie~ (103 points)
0 votes

2x^2 - 11x - 21 = 0

We have 21*2 = 42. So, factorise 42 such that the factors have a differece of 11. Difference because the sign before last term is negative.

So, the factors of 42 which have 11 as their difference are 3*14.

So, we have,

2x^2 - 14x + 3x - 21 = 0

2x(x-7) + 3(x-7) = 0

(x-7)(2x+3) = 0

So, x = 7 and -3/2

answered Dec 5, 2013 by SubjectTeachers1 ~Rookie~ (90 points)



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