How many times does the graph of 4x = 32 - x2 cross the x-axis ?
2 answers:
Answer:
Step-by-step explanation:
● 4x = 32 - x^2
Add x^2 to both sides
● 4x +x^2 = 32 -x^2+x^2
● x^2 +4x = 32
Substract 32 from both sides
● x^2+4x -32 =32-32
● x^2 +4x-32=0
That is a quadratic equation
We will use the determinant method
The determinant is b^2-4ac
● a = 1
● b = 4
● c = 32
● b^2-4ac = 4^2 -4×1×(-32) = 144
144 is positive so the parabola will cross the x-axis two times
● x = (-b -/+ √(b^2-4ac))/2a
● x = (-4 +/- 12) /2
● x = 8/2 or x= -16/2
● x = 4 or x =-8
The solutions are 4 and -8
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I would start by setting up a chart like I did below.
Label one column age now and the other age in 5 years.
Since we don't know the son's age we use x.
We do know that the man's age is 4 times the son's age.
So the man's age will be 4x.
In the age in 5 year column, we add 5 to their current ages.
Now set up our equation.
Since it says "in five years" we use information in second column.
In 5 years time, he, "4x + 5", will be, equals,
3 times as old as his son, "3(x + 5)".
So we have 4x + 5 = 3(x + 5).
Solving from here, we find that x = 10.
So the son is 10 and the man is 4 times his age or 40.
