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2 years ago

If x=5,then3x+4x-15 equals

Mathematics

2 answers:

Lera25 [3.4K]2 years ago

6 0

Answer:

Step-by-step explanation:

3x + 4x - 15

3(5)+4(5) - 15

15 + 20 - 15

You can add the oposites

15 + (-15)

= 0

And then you have 20 left. Or add 15 + 20 = 35 then subtract 15 (which equals 20)

Hope this helps!

lubasha [3.4K]2 years ago

5 0

Answer:

Step-by-step explanation:

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If a paper plane is thrown from the top of a 147-foot cliff into the water below, the height of the plane at any given time can

sasho [114]

Answer:

c. 6.5 seconds.

Step-by-step explanation:

We have been given that a a paper plane is thrown from the top of a 147-foot cliff into the water below, the height of the plane at any given time can be determined by the formula $h = -3t^2+147$ , where h is the height of the plane at t seconds.

To find the time, when plane will be at a height of exactly 20.25 feet, we will substitute $h=20.25$ in our given formula and solve for t as:

$20.25= -3t^2+147$

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$-3t^2+147-147=20.25-147$

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$t^2=42.25$

Take square root of both sides:

$t=\pm \sqrt{42.25}$

$t=\pm 6.5$

Since time cannot be negative, therefore, the plane will be at a height of exactly 20.25 feet after 6.5 seconds and option 'c' is the correct choice.

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