Question

if x=1/2-root 3, the value of x³-2x²-7x+5​

Answer 1

Step-by-step explanation:

Correct option is

A

3

Solution:-

x=

2−

3

1

Multiplying the numerator and denominator by the conjugate of the denominator, we have

x=

2−

3

1

×

2+

3

2+

3

=

2

2

−

3

2

2+

3

=

4−3

2+

3

=2+

3

⇒x

2

=(2+

3

)

2

=4+4

3

+3=7+4

3

Now consider the given expression

x

3

−2x

2

−7x+5=x

3

−7x−2x

2

+5

⇒=x(x

2

−7)−2x

2

+5

⇒=(2+

3

)(7+4

3

−7)−2(7+4

3

)+5

⇒=(2+

3

)(4

3

)−14−8

3

+5

⇒=8

3

+12−14−8

3

+5

⇒=3

x

3

−2x

2

−7x+5=m{Given}

∴m=3

Answer 2

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