6x2 + 19x + 10 = 0 find roots of the quadratic equation by the method of completing square
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Answer:
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Step-by-step explanation:
Divide both sides of the equation by 6 to have 1 as the coefficient of the first term :
x2+(19/6)x+(5/3) = 0
Subtract 5/3 from both side of the equation :
x2+(19/6)x = -5/3
Now the clever bit: Take the coefficient of x , which is 19/6 , divide by two, giving 19/12 , and finally square it giving 361/144
Add 361/144 to both sides of the equation :
On the right hand side we have :
-5/3 + 361/144 The common denominator of the two fractions is 144 Adding (-240/144)+(361/144) gives 121/144
So adding to both sides we finally get :
x2+(19/6)x+(361/144) = 121/144
Adding 361/144 has completed the left hand side into a perfect square :
x2+(19/6)x+(361/144) =
(x+(19/12)) • (x+(19/12)) =
(x+(19/12))2
Things which are equal to the same thing are also equal to one another. Since
x2+(19/6)x+(361/144) = 121/144 and
x2+(19/6)x+(361/144) = (x+(19/12))2
then, according to the law of transitivity,
(x+(19/12))2 = 121/144
We'll refer to this Equation as Eq. #5.2.1
The Square Root Principle says that When two things are equal, their square roots are equal.
Note that the square root of
(x+(19/12))2 is
(x+(19/12))2/2 =
(x+(19/12))1 =
x+(19/12)
Now, applying the Square Root Principle to Eq. #5.2.1 we get:
x+(19/12) = √ 121/144
Subtract 19/12 from both sides to obtain:
x = -19/12 + √ 121/144
Since a square root has two values, one positive and the other negative
x2 + (19/6)x + (5/3) = 0
has two solutions:
x = -19/12 + √ 121/144
or
x = -19/12 - √ 121/144
Note that √ 121/144 can be written as
√ 121 / √ 144 which is 11 / 12