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algebra : graphical solutions
 
 

 

 

A 'straight line intersecting straight line' is dealt with in the 'simultaneous equations' section here

Vertical line intersecting a quadratic curve

Example Find the point of intersection when the vertical at x=-2 meets the curve,

equation#1

graph#10

Substitute the value of x=-2 into the quadratic equation to find y.

equations5

hence the point of intersection is (-2, -3)

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Horizontal line intersecting a quadratic curve

Example - Find the two points of intersection when the horizontal at y=4 meets the curve,

equation#1

graph#6

To find the two points, put one equation equal to the other, rearrange putting zero on one side and find the roots.

equation#2

The roots are complex, therefore we use the quadratic equation formula:

the quadratic equation formula

equation#4

The two points of intersection are (1.828, 4) and (-3.828, 4)

N.B. the rounding of square roots makes the answers only approximate

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Angled straight line intersecting a quadratic curve

Example - Find the points of intersection when the straight line with equation,

equation#6

meets the curve,

equation#1

gaph11

As with the horizontal line intersection , the solution is to put one equation equal to the other, rearrange, put zero on one side and find the roots.

equation#8

The two points of intersection are(0.76, -0.93) and (-1.99, 2.99)

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Straight line intersecting a circle

Example - Find the points of intersection when the straight line with equation,

equation#9

meets the circle with equation,

equation#10

graph#13

The solution is to take the y-value from the straight line equation and put it into the y-value of the circle equation. Then solve for x.

equation#11

The two points of intersection are(2.68, 1.34) and (-2.68, -1.34)

 

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vertical line & quadratic curve

 
  straight line and circle