Question

The roots of x² + bx – 3 = 5 are m and m² respectively, then find the value of b.
1. -3
2. 5
3. -2
4. 2

Answer 1

Correct Answer - Option 3 : -2

Given:

x² + bx – 3 = 5

⇒ x² + bx – 8 = 0

Formula used:

We know that for a quadratic equation ax² + bx + c = 0

Sum of roots = - b/a

Product of roots = c/a

Calculation:

Considering the given equation

x² + bx – 8 = 0

Roots of the given equation are ‘m’ and ‘m²’

Now,

m + m² = – b     ----(i)

m × m² = – 8

⇒ m³ = - 8

⇒ m = – 2

Putting the value of m in equation (i), we get,

⇒ - 2 + (- 2)² = – b

⇒ - b = - 2 + 4

⇒ - b = 2

⇒ b = -2

∴ Required value is – 2