Answer:
y = -2*x² + 60*x
Step-by-step explanation:
The general form of a quadratic function is:
y = a*x² + b*x + c
We need to determine a ; b ; and c. For that we have three conditions therefore
Condition 1 at x = 12 $ each T-shirts kimmie sells 36 units, then she gets
12* 36 = 432 $ or y = 432 and
432 = a(12)² + 12*b + c or 432 = 144*a + 12*b + c
Second condition selling at 13 $ each T-shirt she sells 34 , then
13*34 = 442
442 = a(13)² + 13*b + c or 442 = 169*a + 13*b + c
And the third condition
11*38 = 418
418 = a* ( 121) + 11*b + c 418 = 121*a + 11*b + c
We have a three equation system
432 = 144*a + 12*b + c (1)
442 = 169*a + 13*b + c (2)
418 = 121*a + 11*b + c (3)
We need to solve it for a, b and c
Subtracting (2) - (1) 10 = 25*a + b and subtracting (2) - (3)
24 = 48*a + 2*b
Then b = 10 - 25*a and 24 = 48*a + 2*( 10 - 25*a )
24 = 48*a + 20 - 50*a
24 - 20 = -2*a
4 = - 2*a
a = - 2 and b = 10 - 25*( -2) b = 60
Finally c is: 432 = 144*a + 12*b + c
432 = 144* ( -2) + 12*60 + c
432 = - 288 + 720 + c
432 = 432 + c
c = 0
The quadratic function is:
y = -2*x² + 60*x
