If 5 is one root of x2 - (a - 1)x + 10 = 0, then the other root is:
- AOption (a)
4
- BOption (b)
1
- COption (c)
6
- DOption (d)
2
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Correct answer
2
Why this answer is correct
Shortcut Trick
The product of the roots of a standard quadratic equation of the form x2 − Bx + C = 0 is equal to the constant term C.
Here, the constant term in the given equation is 10.
One of the roots is given as 5.
Other root = Product of roots ÷ Given root = 10 ÷ 5 = 2.
∴ The correct answer is 2.
Alternate Method
Given:
Quadratic equation: x2 − (a − 1)x + 10 = 0
One root of the equation (α) = 5
Formula Used:
For a standard quadratic equation Ax2 + Bx + C = 0, the product of the roots (α × β) is given by C/A.
Calculations:
Let the roots of the equation be α and β.
We are given that α = 5.
Comparing the given equation with the standard form, we get A = 1 and C = 10.
⇒ α × β = C ÷ A
⇒ 5 × β = 10 ÷ 1
⇒ 5 × β = 10
⇒ β = 10 ÷ 5
⇒ β = 2
Thus, the other root of the quadratic equation is 2.
∴ The correct answer is 2.
Additional Information
Sum of Roots
For any quadratic equation ax2 + bx + c = 0, the sum of the roots is equal to −b/a.
Product of Roots
The product of the roots of a quadratic equation ax2 + bx + c = 0 is equal to c/a.
Discriminant and Nature of Roots
The nature of the roots depends on the discriminant D = b2 − 4ac. Roots are real and distinct if D > 0, real and equal if D = 0, and complex conjugates if D < 0.


