Question

Find the value of c that completes the square. r^2+21r+c

Answer 1

c = 110.25

(r + 10.5)²

Explanation:

Hello!

Perfect Square Trinomial:
`(a + b)^2 = a^2 + 2ab + b^2`

21r is basically 2 times r and b, the missing number.

Solve for b

• 21r = 2*r*b
• 10.5 = b

The missing number, b, would be 10.5

Now c is basically b², so we just have to simplify 10.5²:

• 10.5²
• 110.25

c should be 110.25 for it to be a Perfect Square Trinomial. The factored form would be (r + 10.5)².