# What number should be added to the expression x^{2 }+ 4x to change it into a perfect square trinomial?

A polynomial that has only three terms is called a trinomial. It is in the form of x^{2 }+ zx + 1.

## Answer: The number 4 should be added to the expression x^{2 }+ 4x to change it into a perfect square trinomial.

Let's find the number.

**Explanation:**

A function that can be obtained by squaring the binomial expression is a perfect square trinomial. It satisfies the condition b^{2 }- 4ac = 0 and are in the form of ax^{2} + bx + c.

As per the question, b = coefficient of x, a = coefficient of x^{2} and c = constant term.

⇒ b^{2 }- 4ac = 0

⇒ b^{2 }= 4ac

⇒ (4)^{2 }= 4 (1) c

⇒ 16^{ }= 4 × c

By dividing both the sides by 4, we get

⇒ c = 4