A ball is thrown from an initial height of 4 feet with an initial upward velocity of 21/fts. The ball's height h (in feet) after t seconds is given by the following.
h=4+21t-16t^2
Find all values of t for which the ball's height is 10 feet.Round your answer(s) to the nearest hundredth.
(If there is more than one answer, use the "or" button.)

Question

A ball is thrown from an initial height of 4 feet with an initial upward velocity of 21/fts. The ball's height h (in feet) after t seconds is given by the following.
h=4+21t-16t^2
Find all values of t for which the ball's height is 10 feet.Round your answer(s) to the nearest hundredth.
(If there is more than one answer, use the "or" button.)

princesssleelee · Answer

|dw:1466719846611:dw|

kinged · Answer

Equate the equation to 10, and solve for t.

princesssleelee · Answer

what do you mean 'equate'? @Kinged

oops · Answer

he means set it equal to

kinged · Answer

Make it equal to 10.

princesssleelee · Answer

10=4+21t-16t^2

kinged · Answer

Yep.

princesssleelee · Answer

t= 0.89, 0.42

kinged · Answer

Nope. Use quadratic formula and take care of the signs.

kinged · Answer

You'll find two answers: one positive and one negative. Dismiss the negative and take the positive to court.

princesssleelee · Answer

is it going to be a fraction with a square root in it? @Kinged

kinged · Answer

Just show your answer.

princesssleelee · Answer

$$t=\frac{ 21\pm \sqrt{57} }{32  }$$

kinged · Answer

Your answer should be in decimal.

kinged · Answer

Again, you'll find two answers: one positive and one negative. Dismiss the negative and take the positive to court.

princesssleelee · Answer

I have no idea....

kinged · Answer

Evaluate the expression with a plus sign, then evaluate it again with a minus sign.

kinged · Answer

That's what the plus/minus sign means.

princesssleelee · Answer

10=4+21t-16t^2
-10=""

princesssleelee · Answer

0.89, -0.48

kinged · Answer

Use this: http://www.math.com/students/calculators/source/quadratic.htm

kinged · Answer

Substitute the values accordingly and that's about it.

princesssleelee · Answer

i have no idea what that grid was asking for me to fill in , im equaling to 10 as they are 0

kinged · Answer

What's the value before t^2? That's A. What's before t? That's B. What's before C? That's the number.

princesssleelee · Answer

-0.23, -1.08

kinged · Answer

Nope. Did you substitute the right values in A, B, and C?

princesssleelee · Answer

well, i thought i did...

kinged · Answer

-16 goes in A, 21 goes in B, and 4 goes in C.

princesssleelee · Answer

i forgot the negative sign for 16

princesssleelee · Answer

-0.16, 1.48

kinged · Answer

Hey! That's it. Dismiss the negative value, now. That is it.

princesssleelee · Answer

0.16, 1.48

kinged · Answer

I clearly typed "dismiss the negative value" not "dismiss the negative sign".

princesssleelee · Answer

so only 1.48

kinged · Answer

Yeah.