SOLUTION: A building has an entry the shape of a parabolic arch 96 ft high and 18 ft wide at the base, as shown below. A parabola opening down with vertex at the origin is graphed on the c

Algebra ->  Trigonometry-basics -> SOLUTION: A building has an entry the shape of a parabolic arch 96 ft high and 18 ft wide at the base, as shown below. A parabola opening down with vertex at the origin is graphed on the c      Log On


   



Question 1135981: A building has an entry the shape of a parabolic arch 96 ft high and 18 ft wide at the base, as shown below.
A parabola opening down with vertex at the origin is graphed on the coordinate plane. The height of the parabola from top to bottom is ninety six feet and its width from left to right is eighteen feet.

Find an equation for the parabola if the vertex is put at the origin of the coordinate system.

Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
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A building has an entry the shape of a parabolic arch 96 ft high and 18 ft wide at the base, as shown below.
A parabola opening down with vertex at the origin is graphed on the coordinate plane. The height of the parabola from top to bottom is ninety six feet and its width from left to right is eighteen feet.
Find an equation for the parabola if the vertex is put at the origin of the coordinate system.
:
width of arch is -9 to +9. y intercept= 96. Using the form ax^2 + bx + c = y
x=-9,y=0. 81a - 9b + 96 = 0
x=+9,y=0. 81a + 9b + 96 = 0
-------------------------------addition eliminates b
resulting: 162a + 0 + 192 = 0
162a = -192
a = -192/162
a = -1.185
the equation: y = -1.185x^2 + 96
:
Looks like this
+graph%28+300%2C+200%2C+-20%2C+20%2C+-20%2C+110%2C+-1.185x%5E2%2B96%29+