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3 years ago

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What are the solutions of the equation 9x^4 – 2x^2 – 7 = 0? Use u substitution to solve.

1 answer:

Debora [2.8K]3 years ago

8 0

$9x^4 - 2x^2 - 7 = 0 \\ \text{substitution: } x^2=t, \ \ t\ \textgreater \ 0\\ 9t^2-2t-7\ \textgreater \ 0 \\ D=b^2-4ac=(-2)^2-4*9*(-7)=4+252 = 256 \\ t_{1,2}= \frac{-bб \sqrt{D} }{2a}= \frac{2б 16 }{18} \\ t_1=- \frac{14}{18} \ \ \ \ \O \\ \boxed{t_2=1} \\ \\x^2=1\\x=б \sqrt{1} \\ x=б1$

Answer: x=-1, x=1

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3 years ago

when a stone falls freely, the time taken to hit the ground varies as the square root of the distance fallen. If it takes four s

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The stone would take approximately 10.107 seconds to fall 500 meters.

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According to the statement of the problem, the following relationship of direct proportionality is built:

$t \propto y^{1/2}$

$t = k\cdot t^{1/2}$

Where:

$t$ - Time spent by the stone, measured in seconds.

$y$ - Height change experimented by the stone, measured in meters.

$k$ - Proportionality constant, measured in $\frac{s}{m^{1/2}}$ .

First, the proportionality constant is determined by clearing the respective variable and replacing all known variables:

$k = \frac{t}{y^{1/2}}$

If $t = 4\,s$ and $y=78.4\,m$ , then:

$k = \frac{4\,s}{(78.4\,m)^{1/2}}$

$k \approx 0.452\,\frac{s}{m^{1/2}}$

Then, the expression is $t = 0.452\cdot y^{1/2}$ . Finally, if $y = 500\,m$ , then the time is:

$t = 0.452\cdot (500\,m)^{1/2}$

$t \approx 10.107\,s$

The stone would take approximately 10.107 seconds to fall 500 meters.

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