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Vinvika [58]
3 years ago
10

A bridge in the shape of an arch connects two cities separated by a river. The two ends of the bridge are located at (–7, –13) a

nd (7, –13), and the center of the arch on the bridge is located at (0, 0). Find the equation of the arch of the bridge.
Mathematics
1 answer:
sdas [7]3 years ago
5 0

Answer:

y=-\dfrac{13}{49}x^2

Step-by-step explanation:

The shape of an arch corresponds to a parabola.

the general equation for a parabola is:

y=ax^2+bx+c

we're given three coordinates: (-7,-13),(7,-13) and (0,0)

so we can plug these values in the general equation to make 3 separate equations:

(x,y) = (-7,-13)

-13=a(-7)^2+b(-7)+c

49a-7b+c=-13

(x,y) = (7,-13)

-13=a(7)^2+b(7)+c

49a+7b+c=-13

(x,y) = (0,0)

0=a(0)^2+b(7)+c

c=0

so we have three equations. and we can solve them simultaneously to find the values of a,b, and c.

we've already found c = 0, let's use substitute it to other equations.

49a-7b+c=-13\quad\Rightarrow\quad49a-7b=-13

49a+7b+c=-13\quad\Rightarrow\quad49a+7b=-13

we can solve these two equation using the elimination method, by simply adding the two equations

\quad\quad49a-7b=-13\\+\quad49a+7b=-13

------------------------------

\quad\quad 98a=-26

\quad\quad a=-\dfrac{13}{49}

Now we can plug this value of a in any of the two equations.

49a-7b=-13

49\left(-\dfrac{13}{49}\right)-7b=-13

-13-7b=-13

-7b=0

b=0

We have the values of a,b, and c. We can plug them in the general equation to find the equation of the arch.

y=\left(-\dfrac{13}{49}\right)x^2+0x+0

y=-\dfrac{13}{49}x^2

49y=-13x^2

This our equation of the arch!

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