Parallel Lines and Angles Calculator
Find all eight angles made by a transversal crossing two parallel lines. Select the known numbered angle and compare equal and supplementary angle groups.
YOUR CALCULATION
Result
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Calculation steps
Work through one step at a time or reveal the complete calculation. The steps use your current inputs.
How to calculate
Vertical angles are equal, and corresponding angles are equal when the two lines are parallel. Adjacent angles on a straight line add to 180°. These rules place the eight angles into two equal-value groups.
θ1=θ3=θ5=θ7; θ2=θ4=θ6=θ8; θ1+θ2=180°
Worked example
If angle 1 is 65°, angles 3, 5 and 7 are also 65°. Angles 2, 4, 6 and 8 are 115°. Angle 1 corresponds to angle 5, while angles 3 and 5 are alternate interior angles.
Assumptions and input details
The lines must be parallel and the transversal must intersect both. The numbered diagram is schematic; its apparent angle is not a measurement of your input. Angles are in degrees, from 0.000001° to 179.999999°. Numbering starts at the upper-right region of the top crossing and runs counterclockwise; the lower crossing uses the same order for angles 5–8.
Using this calculator
Can I enter my own problem?
Yes. Replace the example values with your own inputs. The result, calculation steps, tables and applicable diagrams update from those inputs. Blank or invalid values clear the result; example values are never silently substituted for missing inputs.
Are the results exact?
Results use floating-point arithmetic and displayed rounding. Read the formula, assumptions and any stated data precision before interpreting the result.
Is my input uploaded?
The calculation runs in your browser. No account, file upload or external AI service is required. Inputs are not saved between page reloads.
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