Find the values of b for which the quadratic equation 4x² + bx + 1 = 0 has equal roots.

Correct option is B

​Given:

​$$4x^2 + bx + 1 = 0$$​​

Formula Used: 

In a quadratic equation
Equal roots when:

​$$b^2 - 4ac = 0$$​​

Solution: 

$$4x^2 + bx + 1 = 0$$​
Here, a = 4, c = 1: 

So, 

​$$b^2 - 4(4)(1) = 0 \\ \ \\ b^2 = 16 \\ \ \\ \implies b = \pm 4$$​​