Let
x and
y be the desired real numbers. Using the given information, we can write two equations, one for the sum of the numbers and one for the product of the numbers.
Sum: Product: x+y=-15xy=-54
We can solve this using the . First, let's isolate
y in the first equation and then substitute it into the second equation.
{x+y=-15xy=-54(I)(II)
{y=-15−xxy=-54
{y=-15−xx(-15−x)=-54
{y=-15−x-15x−x2=-54
{y=-15−x-15x−x2+54=0
{y=-15−x-x2−15x+54=0
Our next step is to solve the obtained .
-x2−15x+54=0⇕-1x2+(-15)x+54=0
We can do this by graphing. Let's begin by finding the of the using the formula
x=-2ab. For our equation, we have that
a = -1 and
b = -15.
x=-2ab
x=-2(-1)-15
x=-7.5
Next, we will make a table of values using
x values around the axis of symmetry
x=-7.5.
x
|
-x2−15x+54
|
y
|
-18
|
-(-18)2−15(-18)+54
|
0
|
-16
|
-(-16)2−15(-16)+54
|
38
|
-7.5
|
-(-7.5)2−15(-7.5)+54
|
110.25
|
1
|
-(1)2−15(1)+54
|
38
|
3
|
-(3)2−15(3)+54
|
0
|
Now, we will plot and connect the obtained points.
The roots of the equation are
-18 and
3. Let's investigate if they satisfy the original problem.
Sum:Product: -18+3=-15 ✓ -18(3)=-54 ✓
Since the numbers satisfy both requirements stated in the exercise we have found the numbers we are looking for, and they are
-18 and
3.