Saturday, February 4, 2012

Solve for x: (3x+7)(x-1)=24.

To solve for x:
(3x+7)(x-1)=24.


We expand left  and rewrite the
equation:


3x(x-1)+7(x-1) =
24.


3x^2-3x+7x-7 =
24.


=> 3x^2 +4x-7-24 =
0.


=> 3x^2 +4x-31 =
0....(1).


This is in the form of ax^2+bx+c = 0 whose
solution is given by:


x1 = (-b+sqrt(b^2-4ac)}/2a
and


x2 =
(-b-sqrt(b^2-4ac)}/2a.


Here in equation at (1): a = 3, b= 4
and c = -31.


Therefore x1 = (-4+sqrt(4^2-4*3*-31)}/2*3 =
(-4+sqrt388)/6


=> x1 =
(-2+sqrt97)/3


x2 =
(-2-sqrt97)/3.


Therefore  (-2+sqrt97)/3 and (-2-sqrt97)/3
are the solutions.

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