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Mekhanik [1.2K]

3 years ago

13

I’d really appreciate help with these...

2 answers:

Irina-Kira [14]3 years ago

7 0

Answer:

+- 5 and +- 3

Step-by-step explanation:

qn 2:

4r² = 91 + 9

4r² = 100

r² = 25

r = +- 5

qn 3:

4r² = 29 + 7

4r² = 36

r² = 9

r = +- 3

vovikov84 [41]3 years ago

4 0

Answer:

<h2>Q2. (±5)</h2><h2>Q3. (±3)</h2>

Step-by-step explanation:

$\bold{Q2.}\\\\4r^2-9=91\qquad\text{add 9 to both sides}\\\\4r^2-9+9=91+9\\\\4r^2=100\qquad\text{divide both sides by 4}\\\\\dfrac{4r^2}{4}=\dfrac{100}{4}\\\\r^2=25\to r=\pm\sqrt{25}\\\\\boxed{r=\pm5}$

$\bold{Q3.}\\\\4r^2-7=29\qquad\text{add 7 to both sides}\\\\4r^2-7+7=29+7\\\\4r^2=36\qquad\text{divide both sides by 4}\\\\\dfrac{4r^2}{4}=\dfrac{36}{4}\\\\r^2=9\to r=\pm\sqrt9\\\\\boxed{r=\pm3}$

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Explanation:

Given that the height, h, in feet of a rock above the ground is given by the equation $h=-16t^2+24t+16$ , where t is the time in seconds after the rock is thrown.

We need to determine the time at which the rock will hit the ground.

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$-16 t^{2}+24 t+16=0$

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