Solve using the quadatric formula...I've been trying to do this but I don't get the correct answer...help!!!!!

Question

6x^2 + 7x- 20= 0

Answer 1

Quadratic Formula: x = [-b +/- V`b^2 - 4ac] / 2a

First: identify 3 terms for 3 variables...
a = 6; b = 7; c = -20

First: replace/substitute the terms with the variables.

x = [-7 +/- V`7^2 - 4(6)(-20)] / 2(6)

x = [-7 +/- V`49 - 4(6)(-20)] / 12

x = [-7 +/- V`49 - 24(-20)] / 12

x = [-7 +/- V`49 + 480] / 12

x = [-7 +/- V`529] / 12

x = [-7 +/- 23] / 12

Third: you have two solutions - addition & subtraction.

a. x = [-7 + 23] / 12
x = 16/12
x = 4/3

b. x = [-7 - 23] / 12
x = -30/12
x = -5/2

Solutions: 4/3 and -5/2

Answer 2

Quadratic Formula
If ax²+bx+c=0 then
x = {-b ±√[b² - 4ac]}/(2a)

6x² + 7x- 20= 0

a = 6
b = 7
c = -20

Plugging these values into the formula
x = {-b ±√[b² - 4ac]}/[2a]
= {-(7) ±√[(7)² - (4)(6)(-20)]}/[(2)(6)]
= {-7 ±√[49 – (-480)]}/12
= {-7 ±√529}/12
= {-7 ± 23}/12
= 16/12 or -30/12
= 4/3 or –5/2

Ok, this is very straight forward. There are no roots of negative numbers, no large fractions. You are even taking the square root of a perfect square. Go through your work and see where your numbers and mine differ.

I plugged these values back into the original formula and got 0. So these are correct.

Answer 3

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Answer 4

x = [-7 (+/-)root(49 - 4(6)(-20))] / 2(6)

x = [-7 (+/-)root(49 + 480)] / 12

x = [-7 (+/-)root(529)] / 12

x = [-7 + 23]/12 = 16/12 = 4/3

x = [-7 - 23]/12 = -30/12 = -15/6

x = 4/3 or -15/6

You problem may be signs. Make sure that when you put in c into the formula, you put -20, not just 20. And make sure when you multiply -4 times 6 times -20 you get a positive 480.

Answer 5

6x^2+7x-20=0
x=(-7±√(7^2+4*6*20))/12
x=(-7±√(49+480))/12
x=(-7±√529)/12
x=(-7±23)/12
x=(-7-23)/12=-30/12=-5/2
x=(-7+23)/12=16/12=4/3

the solutions are -5/2 & 4/3

Answer 6

6x^2 + 7x - 20 =0

-20 * 6x^2 = -120x^2

factors of -120 x^2

-2x , 60x
-3x , 40x
-4x , 30x
-5x , 24x
-6x , 20x
-8x , 15x

the factors required are -8x and 15 x because:

15x - 8x gives you the middle term of the equation which is + 7x and 15x * -8x = -120x^2 which is equal to the product of the two terms on the either sides of the equation (6x^2 , -20)
so,
6x^2 + 15x - 8x - 20 = 0
6x^2 - 8x + 15x - 20 = 0
2x(3x - 4) + 5(3x - 4) = 0
(2x + 5)(3x - 4) = 0

so
2x + 5 = 0
2x = -5
x = -5/2

or
3x - 4 = 0
3x = 4
x = 4/3

so x = -5/2 or 4/3

sure, you can use the formula x = -b +- sqrt (b^2 - 4ac)/2a

but we generally use them when we are unable to factorize it using the method used above.

Answer 7

A= 6
B= 7
C= -20

-7 plus or minus radical 49 minus -480

-7 plus or minus 23 over 12

16 over 12= 16/12= 4/3

-30 over 12= -2.5

x= 4/3 x=-5/2

Answer 8

[-b +- SQRT(b^2 - 4ac)]/(2a)
[-7 +- SQRT(7^2 - 4(6)(-20))]/(2(6))
[-7 +- SQRT(49 + 480]/12
[-7 +- 23]/12

So, we have two answers:

-30/12 = -2.5 and
16/12 = 4/3 = 1.33

Thus, x = -2.5 or 1.33

Answer 9

x=(-b±√(b²-4ac))/2a
=(-7±√(7²-4(6)(-20)))/2(6)
=(-7±√(49+480))/12
=(-7±√529)/12
=(-7±23)/12
x=16/12=4/3 or x=-30/12=-5/2

Answer 10

a=6
b=7
c= -20
b^2-4ac = 49+480 "this"
sqrt (this)= 23
-b+/-sqrt(this) = -30,16
[-b+/-sqrt(this)]/2a= -5/2, 4/3