Point of intersection is the point where two lines or two curves meet each other. The point of intersection of two lines of two curves is a point. If two planes meet each other then the point of intersection is a line. More precisely it is defined as the common point of both the lines or curves that satisfy both the curves which can be derived by solving the equation of the curves. If we consider two lines a1x + b1y + c1 = 0 and a2x + b2y + c2 = 0 the point of intersection of these two lines is given by:
Derivation of point of intersection of two lines:
If two lines are parallel they never intersect each other:
Sample ProblemsQuestion 1: Find the point of intersection of line 3x + 4y + 5 = 0, 2x + 5y +7 = 0. Solution:
Question 2: Find the point of intersection of line 9x + 3y + 3 = 0, 4x + 5y + 6 = 0. Solution:
Question 3: Check if the two lines are parallel or not 2x + 4y + 6 = 0, 4x + 8y + 6 = 0 Solution:
Question 4: Check if the two lines are parallel or not 3x + 4y + 8 = 0, 4x + 8y + 6 = 0 Solution:
Question 5: Check whether the point (3, 5) is point of intersection of lines 2x + 3y – 21 = 0, x + 2y – 13 = 0. Solution:
Question 6: Check whether the point (2, 5) is point of intersection of lines x + 3y – 17 = 0, x + y – 13 = 0 Solution:
Question 7: Find the point of intersection of lines x = -2 and 3x + y + 4 = 0 Solution:
Article Tags : Point of intersection means the point at which two lines intersect. These two lines are represented by the equation a1x + b1y + c1= 0 and a2x + b2y + c2 = 0, respectively. Given figure illustrate the point of intersection of two lines.
We can find the point of intersection of three or more lines also. By solving the two equations, we can find the solution for the point of intersection of two lines.
The formula of the point of Intersection of two lines is: (x, y) = [ \(\begin{array}{l}\frac{b_{1}c_{2}-b_{2}c_{1}}{a_{1}b_{2}-a_{2}b_{1}}\end{array} \) ,\(\begin{array}{l}\frac{a_{2}c_{1}-a_{1}c_{2}}{a_{1}b_{2}-a_{2}b_{1}}\end{array} \) ]
Question: Find out the point of intersection of two lines x + 2y + 1 = 0 and 2x + 3y + 5 = 0. Solution: Given straight line equations are: x + 2y + 1 = 0 and 2x + 3y + 5 = 0 Here, a2 = 2, b2 = 3, c2 = 5 Intersection point can be calculated using this formula, x = \(\begin{array}{l}\frac{b_{1}c_{2}-b_{2}c_{1}}{a_{1}b_{2}-a_{2}b_{1}}\end{array} \) ; y =\(\begin{array}{l}\frac{a_{2}c_{1}-a_{1}c_{2}}{a_{1}b_{2}-a_{2}b_{1}}\end{array} \) (x,y) = ( \(\begin{array}{l}\frac{2\times5-3\times1}{1\times3-2\times2}\end{array} \) ,\(\begin{array}{l}\frac{2\times1-1\times5}{1\times3-2\times2}\end{array} \) )(x,y) = ( \(\begin{array}{l}\frac{10-3}{3-4}\end{array} \) ,\(\begin{array}{l}\frac{2-5}{3-4}\end{array} \) )(x,y) = (-7, 3)
The point of intersection
of two non-parallel
lines can be found from the Try this Drag any of the 4 points below to move the lines. Note where they intersect. To find the intersection of two straight lines:
ExampleSo for example, if we have two lines that have the following equations (in slope-intercept form):y = 3x-3 y = 2.3x+4 At the point of intersection they will both have the same y-coordinate value, so we set the equations equal to each other:3x-3 = 2.3x+4 This gives us an equation in one unknown (x) which we can solve: Re-arrange to get x terms on left3x - 2.3x = 4+3 Combining like terms0.7x = 7 Givingx = 10 To find y, simply set x equal to 10 in the equation of either line and solve for y: Equation for a line (Either line will do)y = 3x - 3 Set x equal to 10y = 30 - 3 Givingy = 27 We now have both x and y, so the intersection point is (10, 27) Recall that lines can be described by the slope/intercept form and point/slope form of the equation. Finding the intersection works the same way for both. Just set the equations equal as above. For example, if you had two equations in point-slope form:y = 3(x-3) + 9 y = 2.1(x+2) - 4 simply set them equal:3(x-3) + 9 = 2.1(x+2) - 4 and proceed as above, solving for x, then substituting that value into either equation to find y.The two equations need not even be in the same form. Just set them equal to each other and proceed in the usual way. When one of the lines is vertical, it has no defined slope, so its equation will look something likex=12 . See Vertical lines (Coordinate Geometry). We find the intersection slightly differently. Suppose we have the lines whose equations are
Equation for a line: y = 3x - 3 Set x equal to 12 Using the equation of the second (vertical) liney = 36 - 3 Givingy = 33 So the intersection point is at (12,33).If both lines are vertical, they are parallel and have no intersection (see below). When two lines are parallel, they do not intersect anywhere. If you try to find the intersection, the equations will be an absurdity. For example the linesy=3x+4 andy=3x+8 are parallel because their slopes (3) are equal. See Parallel Lines (Coordinate Geometry). If you try the above process you would write3x+4 = 3x+8 . An obvious impossibility.
Fig 1. Segments do not intersect In the case of two non-parallel lines, the intersection will always be on the lines somewhere. But in the case of line segments or rays which have a limited length, they might not actually intersect. In Fig 1 we see two line segments that do not overlap and so have no point of intersection. However, if you apply the method above to them, you will find the point where they would have intersected if extended enough. Things to try
LimitationsIn the interest of clarity in the applet above, the coordinates are rounded off to integers and the lengths rounded to one decimal place. This can cause calculatioons to be slightly off. For more see Teaching Notes Other Coordinate Geometry topics (C) 2011 Copyright Math Open Reference. |