# Quadratic formula ?

##### 2 Answers

Alex will land

#### Explanation:

We seek to find

#0 = -3.9d^2 + 13.1d + 8.7#

Now apply the quadratic formula.

#d = (-13.1 +- sqrt(13.1^2 - 4 * -3.9 * 8.7))/(2 * -3.9)#

#d = (-13.1 +- sqrt(307.33))/(-7.8)#

We now use a calculator.

#d = 3.927 m or -0.568# m

A negative answer is clearly impossible so Alex will land

Hopefully this helps!

#### Explanation:

It's stated in this problem that Alex's path can be modelled by the quadratic function

The maximum value of this function will be the maximum height reached by Alex.

In order to find the maximum value of

Now, the expression

Multiplying this expression by

Let's add

This expression is now equivalent to our function

According to this inequality, the function

Rounding this number to the nearest tenth gives

Therefore, Alex reaches no higher than