Mathematics » High School: Geometry » Similarity, Right Triangles, & Trigonometry

Standards in this domain:

Understand similarity in terms of similarity transformations

  • G-SRT.1. Verify experimentally the properties of dilations given by a center and a scale factor:
    • A dilation takes a line not passing through the center of the dilation to a parallel line, and leaves a line passing through the center unchanged.
    • The dilation of a line segment is longer or shorter in the ratio given by the scale factor.
  • G-SRT.2. Given two figures, use the definition of similarity in terms of similarity transformations to decide if they are similar; explain using similarity transformations the meaning of similarity for triangles as the equality of all corresponding pairs of angles and the proportionality of all corresponding pairs of sides.
  • G-SRT.3. Use the properties of similarity transformations to establish the AA criterion for two triangles to be similar.

Prove theorems involving similarity

  • G-SRT.4. Prove theorems about triangles. Theorems include: a line parallel to one side of a triangle divides the other two proportionally, and conversely; the Pythagorean Theorem proved using triangle similarity.
  • G-SRT.5. Use congruence and similarity criteria for triangles to solve problems and to prove relationships in geometric figures.

Define trigonometric ratios and solve problems involving right triangles

  • G-SRT.6. Understand that by similarity, side ratios in right triangles are properties of the angles in the triangle, leading to definitions of trigonometric ratios for acute angles.
  • G-SRT.7. Explain and use the relationship between the sine and cosine of complementary angles.
  • G-SRT.8. Use trigonometric ratios and the Pythagorean Theorem to solve right triangles in applied problems.

Apply trigonometry to general triangles

  • G-SRT.9. (+) Derive the formula A = 1/2 ab sin(C) for the area of a triangle by drawing an auxiliary line from a vertex perpendicular to the opposite side.
  • G-SRT.10. (+) Prove the Laws of Sines and Cosines and use them to solve problems.
  • G-SRT.11. (+) Understand and apply the Law of Sines and the Law of Cosines to find unknown measurements in right and non-right triangles (e.g., surveying problems, resultant forces).