Which option shows the correct substitution of values into the quadratic formula for the equation 2p

2
−7p−13=0?

p=
2
(−7)±
(7)
2
−4(−2)(−13)





p=
2(2)
−7±
−7
2
−4(2)(13)





p=
2(2)
−(7)±
(7)
2
−4(2)(13)





p=
2(2)
−(−7)±
(−7)
2
−4(2)(−13)


1 answer

To identify the correct substitution of values into the quadratic formula for the equation \(2p^2 - 7p - 13 = 0\), we first need to identify the coefficients \(a\), \(b\), and \(c\) from the standard form of a quadratic equation \(ap^2 + bp + c = 0\).

From the given equation:

  • \(a = 2\)
  • \(b = -7\)
  • \(c = -13\)

The quadratic formula is given by:

\[ p = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \]

Now, substituting the values of \(a\), \(b\), and \(c\) into the formula:

  • For \( -b \): Substitute \(b = -7\). Thus, \(-b = -(-7) = 7\).
  • For \(b^2\): Substitute \(b = -7\), so \(b^2 = (-7)^2 = 49\).
  • For \(4ac\): Substitute \(a = 2\) and \(c = -13\). Therefore, \(4ac = 4(2)(-13) = -104\).

Putting it together, we have:

\[ p = \frac{7 \pm \sqrt{49 - (-104)}}{2(2)} \]

This means we are looking for a substitution of:

  1. The coefficient of p (which was fulfilled by \(-(-7)\) or \(7\)).
  2. The 2 values of \(2a\) which is \(2(2)\).
  3. The values inside the square root where \((-7)^2 - 4(2)(-13)\).

Now let's analyze each option provided:

  1. First option:

    \[ p = \frac{2(-7) \pm \sqrt{(-7)^2 - 4(-2)(-13)}}{2} \] Incorrect substitution of \(a\).

  2. Second option:

    \[ p = \frac{2(2) - 7 \pm \sqrt{(-7)^2 - 4(2)(13)}}{2} \] Incorrect substitution of \(c\).

  3. Third option:

    \[ p = \frac{2(2) - (-7) \pm \sqrt{(-7)^2 - 4(2)(13)}}{2} \] Incorrect substitution of \(c\).

  4. Fourth option:

    \[ p = \frac{2(2) - (-7) \pm \sqrt{(-7)^2 - 4(2)(-13)}}{2} \] Correct substitution. Here \(-(-7)\) correctly gives \(7\) and \(4ac\) is properly given with a negative sign for \(c\).

Thus, the correct substitution is:

Fourth option:

\[ p = \frac{2(2) - (-7) \pm \sqrt{(-7)^2 - 4(2)(-13)}}{2} \]