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Maths Gcse Edexcel Higher

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  1. Scatter-Graphs-And-Correlation Edexcel Higher
    2 主题
  2. Cumulative-Frequency-And-Box-Plots Edexcel Higher
    4 主题
  3. Histograms Edexcel Higher
    3 主题
  4. Statistical-Diagrams Edexcel Higher
    7 主题
  5. Averages-Ranges-And-Data Edexcel Higher
    8 主题
  6. Combined-And-Conditional-Probability Edexcel Higher
    3 主题
  7. Tree-Diagrams Edexcel Higher
    1 主题
  8. Simple-Probability-Diagrams Edexcel Higher
    3 主题
  9. Transformations Edexcel Higher
    5 主题
  10. Vectors Edexcel Higher
    6 主题
  11. 3D-Pythagoras-And-Trigonometry Edexcel Higher
    1 主题
  12. Sine-Cosine-Rule-And-Area-Of-Triangles Edexcel Higher
    4 主题
  13. Pythagoras-And-Trigonometry Edexcel Higher
    4 主题
  14. Area-And-Volume-Of-Similar-Shapes Edexcel Higher
    1 主题
  15. Congruence-Similarity-And-Geometrical-Proof Edexcel Higher
    5 主题
  16. Volume-And-Surface-Area Edexcel Higher
    3 主题
  17. Circles-Arcs-And-Sectors Edexcel Higher
    2 主题
  18. Area-And-Perimeter Edexcel Higher
    4 主题
  19. Circle-Theorems Edexcel Higher
    7 主题
  20. Bearings-Scale-Drawing-Constructions-And-Loci Edexcel Higher
    5 主题
  21. Angles-In-Polygons-And-Parallel-Lines Edexcel Higher
    3 主题
  22. Symmetry-And-Shapes Edexcel Higher
    6 主题
  23. Exchange-Rates-And-Best-Buys Edexcel Higher
    2 主题
  24. Standard-And-Compound-Units Edexcel Higher
    5 主题
  25. Direct-And-Inverse-Proportion Edexcel Higher
    2 主题
  26. Problem-Solving-With-Ratios Edexcel Higher
    2 主题
  27. Ratios Edexcel Higher
    3 主题
  28. Sequences Edexcel Higher
    4 主题
  29. Transformations-Of-Graphs Edexcel Higher
    2 主题
  30. Graphing-Inequalities Edexcel Higher
    2 主题
  31. Solving-Inequalities Edexcel Higher
    2 主题
  32. Real-Life-Graphs Edexcel Higher
    4 主题
  33. Estimating-Gradients-And-Areas-Under-Graphs Edexcel Higher
    2 主题
  34. Equation-Of-A-Circle Edexcel Higher
    2 主题
  35. Graphs-Of-Functions Edexcel Higher
    6 主题
  36. Linear-Graphs Edexcel Higher
    4 主题
  37. Coordinate-Geometry Edexcel Higher
    4 主题
  38. Functions Edexcel Higher
    3 主题
  39. Forming-And-Solving-Equations Edexcel Higher
    3 主题
  40. Iteration Edexcel Higher
    1 主题
  41. Simultaneous-Equations Edexcel Higher
    2 主题
  42. Quadratic-Equations Edexcel Higher
    4 主题
  43. Linear-Equations Edexcel Higher
    1 主题
  44. Algebraic-Proof Edexcel Higher
    1 主题
  45. Rearranging-Formulas Edexcel Higher
    2 主题
  46. Algebraic-Fractions Edexcel Higher
    4 主题
  47. Completing-The-Square Edexcel Higher
    1 主题
  48. Factorising Edexcel Higher
    6 主题
  49. Expanding-Brackets Edexcel Higher
    3 主题
  50. Algebraic-Roots-And-Indices Edexcel Higher
    1 主题
  51. Introduction Edexcel Higher
    7 主题
  52. Using-A-Calculator Edexcel Higher
    1 主题
  53. Surds Edexcel Higher
    2 主题
  54. Rounding-Estimation-And-Bounds Edexcel Higher
    2 主题
  55. Fractions-Decimals-And-Percentages Edexcel Higher
    3 主题
  56. Simple-And-Compound-Interest-Growth-And-Decay Edexcel Higher
    4 主题
  57. Percentages Edexcel Higher
    3 主题
  58. Fractions Edexcel Higher
    4 主题
  59. Powers-Roots-And-Standard-Form Edexcel Higher
    4 主题
  60. Prime-Factors-Hcf-And-Lcm Edexcel Higher
    4 主题
  61. Number-Operations Edexcel Higher
    10 主题
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Exam code:1MA1

Angle in a semicircle

Circle Theorem: The angle in a semicircle is 90°

  • The lines drawn from a point on the circumference to either end of a diameter are perpendicular

    • The angle at that point on the circumference is 90°

    • This circle theorem only uses half of the circle

      • The right-angle is called the angle in a semicircle

  • This is a special case of the circle theorem “the angle at the centre is twice the angle at the circumference”

    • The angle on the diameter is 180°

    • The angle at the circumference is halved, giving 90°

Right angle in a semicicrcle, IGCSE & GCSE Maths revision notes

  • To spot this circle theorem on a diagram look for a triangle where

    • one side is the diameter

      • Remember that a diameter always goes through the centre

    • all three vertices are on the circumference

  • The 90º angle will always be the angle opposite the diameter

  • When explaining this theorem in an exam you must use the keywords: 

    • The angle in a semicircle is 90° 

  • Questions that use this theorem may

    • appear in whole circles or in semicircles

    • require the use of Pythagoras’ Theorem to find a missing length

Worked Example

A circle with points P, Q and R on the circumference. The points are joined to form a triangle inside the circle. The angle PQR is 40º and the angle PRQ is yº.

P, Q and R are points on a circle.
RQ is a diameter.

Find the value of y.

Give a reason for your answer.

Use the fact that angles in a triangle add up to 180º and the circle theorem

The angle in a semicircle is 90°

Write an equation for y

y plus 90 plus 40 equals 180

Solve for y

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