Questions tagged [analytic-geometry]

Questions on the use of algebraic techniques for proving geometric facts. Analytic Geometry is a branch of algebra that is used to model geometric objects - points, (straight) lines, and circles being the most basic of these. It is concerned with defining and representing geometrical shapes in a numerical way.

Analytic geometry, also called coordinate geometry, mathematical subject in which algebraic symbolism and methods are used to represent and solve problems in geometry.

The importance of analytic geometry is that it establishes a correspondence between geometric curves and algebraic equations. This correspondence makes it possible to reformulate problems in geometry as equivalent problems in algebra, and vice versa; the methods of either subject can then be used to solve problems in the other.

Analytic geometry was introduced by René Descartes in $1637$ and was of fundamental importance in the development of the calculus by Sir Isaac Newton and G. W. Leibniz in the late $17^{th}$ cent. More recently it has served as the basis for the modern development and exploitation of algebraic geometry.

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Conics definition from Lens formula

Starting with Lens formula directly $$ \frac1u + \frac1u = \frac1f $$ or in its Gauss form: $$ (u-f)(v-f) = f^2, $$ how to recast this into the conics form using definition of eccentricity $$ \frac{PF}{PD} = e\,, $$ at least as an approximation,…
Narasimham
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Find the locus of foot of perpendicular from origin

A variable line cuts the lines $x^2-(a+b)x+ab=0$ in such a way that intercept between the lines subtends a right angle at the origin. Find the locus of the foot of perpendicular from origin on the variable line. Lines are $x=a$ and $x=b$ and I…
MathGeek
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Finding the Height and line equation of a plain

Create the equation of the median and the height From A where ABC is a triangle, find the angle between median and the height from A. $$A(2, 0); B(1, -2), C(3, 6)$$ Solution: If M is the middle point between A and C it has cordinates M(2, 2). The…
Hajko
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When are the points of intersection of two real affine conics orthogonal to each other?

Show that the lines joining the origin to the points of intersection of two curves $ax^2+2hxy+by^2+2gx=0$ and $a_1x^2+2h_1xy+b_1y^2+2g_1x=0$ will be at right angles to one another if $g(a_1+b_1)=g_1(a+b)$. My approach: $$\begin{eqnarray} \tag {1}…
pi-π
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Find the volume of a tetrahedron

Let $A(2,1,3), B(3,2,5), C(3,3,6), D(4,4,2)$ Find the volume $V$ of tetrahedron $ABCD$. My Solution: $\vec{AB} = (1, 1, 2), \vec{AC} = (1, 2, 3), \vec{AD} = (2, 3, -1)$ $$V=\begin{vmatrix}1&1&2\\1&2&3\\2&3&-1 \end{vmatrix}=-6$$ My question is: Is…
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Prove that the homogeneous equation of second degree..

Prove that every homogeneous equation of second degree in $x$ and $y$ represents a pair of lines, each passing through the origin. My Attempt: Let $ax^2+2hxy+by^2=0$ be a homogeneous equation of second degree in $x$ and $y$. We can write this…
pi-π
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If $a,b,c$ are in Arithmetic Progression, find the other two vertices of the triangle.

A triangle $ABC$ is given where vertex $A$ is $(1,1)$ and the orthocentre is $(2,4)$. Also sides $AB$ and $BC$ are members of the family of the lines $ax+by + c = 0$, where $a,b,c$ are in Arithmetic Progression..Find the other two vertices of the…
MathGeek
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If one of the focii of ellipse is moved to infinity, then how it becomes a parabola?

Eccentricity of Parabola is 1. Eccentricity of ellipse is <1. i.e. FP / PM = 1 for parabola. Then how an ellipse will become a parabola if F1P / PM =e<1 if F1 is any one of its focus?
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Plot points on an arc

I have modified this post with updated information so the problem may be more clear. Because the answer provided does not achieve the results intended, maybe adjusting the content will help adjust the answer...thanks. I'm writing an application,…
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Find the radius of the circle with some given conditions.

A circle having centre at C is made to pass through the point $P(1,2)$ , touching the straight lines $7x - y = 5$ and $x + y +13 = 0$ at A and B respectively. Then find the radius of the circle. I have no clue how to solve this problem. Please help…
Daniel
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Using a single scalar equation to describe a line in space

A line in three-dimensional space may be described as an intesection of two planes, for example: $$\begin{align}x+y+z=0\tag{1}\\3x+7y=1\tag{2}\end{align}$$ This can be understood as two separate scalar equations or as a single matrix equation. (One…
Dejan Govc
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If the reflection of the hyperbola $xy = 4$ in the line $x - y + 1 = 0$ is $xy = mx + ny + l$ find $m + n + l$

If the reflection of the hyperbola $xy = 4$ in the line $x - y + 1 = 0$ is $xy = mx + ny + l$ find $m + n + l$. I already solved it by taking a general point (more than one way possible for it) and then finding the reflection and then substituting…
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the equation of two sides of a parallelogram are $2x-3y+7=0$ and $4x+y-21=0$ and one vertex is $(-1,-3)$. Find the other vertices.

First, I checked if the point $(-1,-3)$ is not a solution to the two given equations above so therefore none of those lines passes that point. Then, I solved for the lines parallel to equations above getting $2x-3y-7=0$ and $4x+y+7=0$…
enggfrosh
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The line $2x-y=5$ turns about a point....

The line $2x-y=5$ turns about a point on it, whose ordinate and abscissae are equal, through an angle of $45°$, in anti clockwise direction. Find the equation of line in the new position. My attempt to solve: Let AB be the line with the equation…
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If $ax^2+2hxy+by^2+2gx+2fy+c=0$, prove that

If $$ax^2+2hxy+by^2+2gx+2fy+c=0,$$ represents a pair of lines, show that the square of the distance from origin to their point of intersection is $$\frac{c(a+b)-f^2-g^2}{ab-h^2}.$$ My attempts; since the given equation represents a pair of straight…