Try this beautiful problem from Algebra based on Quadratic Equation….

## Quadratic equation – AMC-10A, 2005- Problem 10

There are two values of $a$ for which the equation $4 x^{2}+a x+8 x+9=0$ has only one solution for $x$. What is the sum of those values of $a$ ?

- \(5\)
- \(20\)
- \(-16\)
- \(25\)
- \(36\)

**Key Concepts**

algebra

Quadratic equation

Equal roots

## Check the Answer

But try the problem first…

Answer: \(-16\)

AMC-10A (2005) Problem 10

Pre College Mathematics

## Try with Hints

First hint

The given equation is $4 x^{2}+a x+8 x+9=0$

\(\Rightarrow 4 x^{2}+x(a+8)+9=0\)

comparing the above equation with \(Ax^2-Bx+C=0\) we will get \(A=4\),\(B=(a+8)\),\(C=9\)

Now for equal roots of a quadratic equation \(B^2-4Ac=0\)

Can you now finish the problem ……….

Second Hint

Now \(B^2-4Ac=0\) becomes

\((a+8)^2-4\times 9 \times 4=0\)

\(\Rightarrow (a+8)^2=144\)

\(\Rightarrow (a+8)=\pm 12\)

\(\Rightarrow a=+4 \) & \(-20\)

Final Step

Therefore The sum of the values of \(a=-20+4=-16\)

## Other useful links

- https://www.cheenta.com/pentagon-square-pattern-amc-10a-2001-problem-18/
- https://www.youtube.com/watch?v=U_LztQXd12A&t=4s

Google