since the triangles are similar
angle DEC = 60 degrees
3 angles inside a triangle equal 180 degrees
BAC = DCE = 64
CBA = EDC = 56
DEC = 180 -56 -64 = 60 degrees
used angle-angle theorem
Volume of a cylinder = π r² h
Given:
radius = (x+8)
height (2x + 3)
Volume of a cylinder = π * (x+8)² * (2x + 3)
V = π * (x+8)(x+8) * (2x+3)
V = π * (x² + 8x + 8x + 64) * (2x + 3)
V = π * (x² + 16x + 64) * (2x + 3)
V = π * (2x³ + 32x² + 128x + 3x² + 48x + 192)
V = π * (2x³ + 32x² + 3x² + 128x + 48x + 192)
V = π * (2x³ + 35x² + 176x + 192)
First, list all the given information:
*100 miles/week
*25 miles/gallon
*$4/gallon
*weekly expenditure reduced by $5
The easiest approach to use here is the dimensional analysis. Cancel out like units if they appear both in the numerator and denominator side. Solve first the original cost. The solution is as follows:
100 miles/week * 1 gal/25 miles * $4/gal = $16/week
The reduced cost would be:
16 - 5 = (New average miles/week) * 1 gal/25 miles * $4/gal
New average miles/week = 68.75 miles/week
In the general case in Cartesian coordinates, you would use the definition of a parabola as the locus of points equidistant from the focus and directrix. The equation would equate the square of the distance from a general point (x, y) to the focus with the square of the distance from that point to the directrix line.
Suppose the focus is located at (h, k) and the equation of the directrix is ax+by+c=0. The expression for the square of the distance from (x, y) to the point (h, k) is ...
(d₁)² = (x-h)²+(y-k)²
The expression for the square of the distance from (x, y) to the directrix line is
(d₂)² = (ax+by+c)²/(a²+b²)
Equating these expressions gives the equation of the parabola.
(x-h)²+(y-k)² = (ax+by+c)²/(a²+b²)
When the directrix is parallel with one of the axes, one of the coefficents "a" or "b" is zero and the equation becomes much simpler. Often, it would be easier to make use of the formula (for a directrix parallel to the x-axis):
y = 1/(4p)*(x -h)² +k
where the (h, k) here is the vertex, the point halfway between the focus and directrix, and "p" is the (signed) distance from the focus to the vertex. (p is positive when the focus is above or to the right of the vertex.)
