Question

Can you explain the method that you used for this quadratic, and why did you choose the method?

Answer 1

The given quadratic equation is

`0=-16x^2+64x+80`

At first switch the 2 sides

`-16x^2+64x+80=0`

Divide all terms by -16 to simplify it

`\begin{gathered} (-16x^2)/(-16)+(64x)/(-16)+(80)/(-16)=(0)/(-16) \\ \\ x^2-4x-5=0 \end{gathered}`

Now, we need to factor the lift side

`\begin{gathered} x^2=(x)(x) \\ -5=(1)(-5) \\ (x)(1)+(x)(-5)=x-5x=-4x \\ x^2-4x-5=(x+1)(x-5) \end{gathered}`

Then the equation is

`(x+1)(x-5)=0`

Equate each factor by 0 to find x

`\begin{gathered} x+1=0 \\ x+1-1=0-1 \\ x=-1 \end{gathered}`
`\begin{gathered} x-5=0 \\ x-5+5=0+5 \\ x=5 \end{gathered}`

Since the time can not be a negative value, then we will refuse x = -1

The stick hit the ground after 5 seconds