Question

A ball is thrown into the air. A sensor measures the height of the ball above the ground. the height of the ball is described by the equation: y=-5x(x-4), where x represents the time in seconds. determine the intervals of time when the ball is above a height of 15meters.

Answer 1

will fan and medal for answer

Answer 2

There are two options with this equation, one is you can graph it on a graphing calculator and find what x is when you put 15 for y, but since most graphing calculators don't let you input for a zero for y solve it like this.

Set 15=y because it asks for what the time (x) is when the ball is 15 m above the ground. So your new equation is
15= -5x(x-4)
now simplify
15=-5x^2+20x
subtract 15 from both sides
-5x^2+20x-15=0
factor the equation
(5x+15)(x-1)=0
Then solve for each factored part for x
5x+15=0
5x=-15
x=-3
x-1=0
x=1
since -3 seconds is not possible in our world, x= 1 so after 1 second the ball will reach 15 meters.

If you put in y=-5x^2+20 into a graphing calculator you should get the same answer.

Good Luck, Hope I helped :)

Answer 3

Could you fan? @Twiztidsplifff

Answer 4

nitely

Answer 5

I think @I_Need_Help_With_Home is correct, she explained it really good