Question

${x }^{2} - 3x - 4 = 0 \: by \: formula \: method$
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Answer 1

Answer:

10th

Maths

Quadratic Equations

Solutions of Quadratic Equations

Solve: x^2 - 3x - 4 = 0?

MATHS

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Asked on December 20, 2019 by

Pavithra Camp

Solve:x

2

−3x−4=0?

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ANSWER

Given,

x

2

−3x−4=0

⇒x

2

−3x−4+4=4

⇒x

2

−3x=4

To make a trinomial square on the left side of the equation, We have to find a value that is equal to the square of half of b, the coefficient of x.

So, (

2

b

)

2

=(−

2

3

)

2

Adding the term to both sides of the equation,

x

2

−3x+(−

2

3

)

2

=4+(−

2

3

)

2

⇒x

2

−3x+

4

9

=

4

25

⇒x

2

+2⋅x⋅(−

2

3

)+(−

2

3

)

2

=

4

25

⇒(x−

2

3

)

2

=

4

25

Taking square root of both sides we get,

(x−

2

3

)

2

=±

4

25

⇒x−

2

3

=±

2

5

For

2

5

,x−

2

3

=

2

5

⇒x=

2

5

+

2

3

=4

For −

2

5

,x−

2

3

=−

2

5

⇒x=−

2

5

+

2

3

=−1

Hence, the solution is x=4