what are the horizontal intercepts for this equation?

Question

y=-40t²+225t

Answer 1

You want the x-intercept.  Set y=0 and solve for t.

 

0 = -40t² + 225t

 

0 = -10t(4t - 22.5)

 

Set the factors equal to zero and solve for t.

Answer 2

y = -40t² + 225t

 

Take out the greatest common factor, -5t:

 

y = -5t(8t - 45)

0 = -5t(8t - 45)

 

-5t = 0

t = 0

 

8t - 45 = 0

8t = 45

t = 45/8 (= 5 ⁵/₈)

Answer 3

Solve for t in

 

-40t² + 225t = 0

 

One solution is t = 0 (by inspection).

 

Do you know how to find the other solution by factoring or using the quadratic formula?