Quadratic Equation
- If a and b are the roots of the equation x2 - 6x + 6 = 0, find the value of 2(a2 + b2).
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a and b are the roots of the equation
x2 - 6x + 6 = 0
∴ a + b = -B/A = 6 and ab = C/A = 6Correct Option: C
a and b are the roots of the equation
x2 - 6x + 6 = 0
∴ a + b = -B/A = 6 and ab = C/A = 6
We know that,
a2 + b2 = (a + b)2 - 2ab
= (6)2 - 2 x 6 = 36 - 12 = 24
∴ 2(a2 + b2) = 2 x 24 = 48
- If α, β are the roots of the equation x2 - 5x + 6 = 0, construct a quadratic equation whose roots are
1 , 1 . α β
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As per the given above question , we can say that
Comparing x2 - 5x + 6 = 0 with ax2 - bx + c = 0 , we get
a = 1, b = - 5, c = 6∴ α + β = - b = 5 = 5 a 1 αβ = c = 6 a
Now, we are to form an equation whose roots are1 , 1 . α β Correct Option: C
As per the given above question , we can say that
Comparing x2 - 5x + 6 = 0 with ax2 - bx + c = 0 , we get
a = 1, b = - 5, c = 6∴ α + β = - b = 5 = 5 a 1 αβ = c = 6 a
Now, we are to form an equation whose roots are
So the required equation is1 , 1 . α β
x2 − (sum of roots)x + (Product of roots) = 0x2 1 + 1 x + 1 . 1 = 0 α β α β x2 - α + β x + 1 = 0 αβ αβ x2 - 5 x + 1 = 0 6 6
6x2 - 5x + 1 = 0
Thus , required equation is 6x2 - 5x + 1 = 0 .
- Consider the equation px2 + qx + r = 0, where p, q, r are real. The roots are equal in magnitude but opposite in sign when :
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As per the given above question , we can say that
Let, the roots be α and −α. Then, sum of roots = 0 Also, roots being not equal, discriminant ≠ 0∴ q = 0 and q2 - 4pr ≠ 0 p Correct Option: D
As per the given above question , we can say that
Let, the roots be α and −α. Then, sum of roots = 0 Also, roots being not equal, discriminant ≠ 0
⟺ q = 0 and pr ≠ 0.∴ q = 0 and q2 - 4pr ≠ 0 p
- The roots of the equation 4x - 3 × 2x × 22 + 32 = 0 would include :
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According to question , we have
Given equation is :- 22x - 3 × 2x × 22 + 32 = 0
⇒ 22x - 12 × 2x + 32 = 0
⇒ y2 - 12y + 32 = 0, where 2x = yCorrect Option: D
According to question , we have
Given equation is :- 22x - 3 × 2x × 22 + 32 = 0
⇒ 22x - 12 × 2x + 32 = 0
⇒ y2 - 12y + 32 = 0, where 2x = y
⇒ ( y - 8 ) ( y - 4 ) = 0
⇒ y = 8, y = 4
∴ 2x = 8 or, 2x = 4
⇒ 2x = 23 or, 2x = 22
⇒ x = 3 or, x = 2.
Therefore , the roots of the equation are 3 and 2.
- Find the value of k so that the sum of the roots of the equation 3x2 + (2x + 1)x - k - 5 = 0 is equal to the product of the roots :
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The given equation is 3x2 + (2k + 1)x - k - 5 = 0
Compare with ax2 + bx + c = 0, we get
a = 3, b = 2k + 1, c = - k - 5∴Sum of the roots = - b = - ( 2k + 1 ) a 3 Correct Option: A
The given equation is 3x2 + (2k + 1)x - k - 5 = 0
Compare with ax2 + bx + c = 0, we get
a = 3, b = 2k + 1, c = - k - 5∴Sum of the roots = - b = - ( 2k + 1 ) a 3
According to question ,and Product of the roots = c = - k - 5 = - ( k + 5 ) a 3 3
∵ Sum of the roots = Product of the roots
⇒ 2k + 1 = k + 5∴ - ( 2k + 1 ) = - ( k + 5 ) 3 3
⇒ 2k - k = 5 - 1
⇒ k = 4.
Therefore , the value of k is 4 .