SOLUTION: Hi all, I was hoping someone could show me how to solve the following quadratic equation: I need to solve for t 0 = 3t^2 + 4t - 24 Help with full working and steps with notes w

Algebra ->  Quadratic Equations and Parabolas -> SOLUTION: Hi all, I was hoping someone could show me how to solve the following quadratic equation: I need to solve for t 0 = 3t^2 + 4t - 24 Help with full working and steps with notes w      Log On


   



Question 208967: Hi all, I was hoping someone could show me how to solve the following quadratic equation:
I need to solve for t
0 = 3t^2 + 4t - 24
Help with full working and steps with notes would be most appreciated.
-nick.

Answer by Edwin McCravy(20056) About Me  (Show Source):
You can put this solution on YOUR website!
I need to solve for t

0+=+3t%5E2+%2B+4t+-+24

3t%5E2+%2B+4t+-+24=0

There are two ways, completing the square
and quadratic formula.

COMPLETING THE SQUARE:
Get all variable terms on the left and
the constant term on the right:

3t%5E2+%2B+4t+=+24

Divide through by the coefficient of t%5E2

%283%2F3%29t%5E2%2B%284%2F3%29t=24%2F3

++t%5E2%2B%284%2F3%29t=8+

Multiply coefficient of t by 1%2F2:  %284%2F3%29%281%2F2%29=2%2F3
Square that: %282%2F3%29%5E2=4%2F9
Add 4/9 to both sides:

t%5E2%2B%284%2F3%29t%2B4%2F9=8%2B4%2F9

Factor left side, get LCD on the right:

%28t%2B2%2F3%29%28t%2B2%2F3%29=72%2F9%2B4%2F9

%28t%2B2%2F3%29%5E2=76%2F9

Take square roots of both sides, remembering ± on the right

sqrt%28%28t%2B2%2F3%29%5E2%29=%22%22%2B-sqrt%2876%2F9%29

t%2B2%2F3=%22%22%2B-sqrt%2876%29%2Fsqrt%289%29

t%2B2%2F3=%22%22%2B-sqrt%2876%29%2F3

Add -2%2F3 to both sides:

t=-2%2F3%2B-sqrt%2876%29%2F3

Break up 76 by observing that it can
be divided by perfect square 4, so
76=4*19

t=-2%2F3%2B-sqrt%284%2A19%29%2F3

t=-2%2F3%2B-sqrt%284%29sqrt%2819%29%2F3

t=-2%2F3+%2B-+2sqrt%2819%29%2F3

So the two solutions are

t=-2%2F3%2B2sqrt%2819%29%2F3 and t=-2%2F3-2sqrt%2819%29%2F3


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QUADRATIC FORMULA

The solution to ax%5E2%2Bbx%2Bc=0 is

x+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+ 

with x=t, a=3, b=4, c=-24

  

t+=+%28-4+%2B-+sqrt%2816%2B+288+%29%29%2F6+ 

t+=+%28-4+%2B-+sqrt%28304+%29%29%2F6+

t+=+%28-4+%2B-+sqrt%2816%2A19+%29%29%2F6+

t+=+%28-4+%2B-+sqrt%2816%29sqrt%2819%29+%29%2F6+

t+=+%28-4+%2B-+4sqrt%2819%29+%29%2F6+

Make two fractions:

t+=+-4%2F6+%2B-+4sqrt%2819%29+%2F6+

Reduce the fractions by dividing top and bottom by 2:

t+=+-2%2F3+%2B-+2sqrt%2819%29+%2F3+

So the two solutions are

t=-2%2F3%2B2sqrt%2819%29%2F3 and t=-2%2F3-2sqrt%2819%29%2F3

Same answer.

Edwin