Geometry Notes Lesson 4.3B – Similarity and Scale Drawings T.2.G.1 Apply congruence (SSS …) and similarity (AA …) correspondences and properties of figures to find missing parts of geometric figures and provide logical justification M.3.G.4 Use (given similar geometric objects) proportional reasoning to solve practical problems (including scale drawings) M.3.G.5 Use properties of parallel lines and proportional reasoning to find the lengths of segments CGT.5.G.5 Draw and interpret the results of transformations and successive transformations on figures in the coordinate plane translations reflections rotations (90˚, 180˚, clockwise and counterclockwise about the origin) dilations (scale factor)

Example 1 The blueprint of a new school building has a 1 cm: 20 m ratio. If the blue print shows the distance across the front of the building to be 3.5 cm, what is the actual distance across the front of the building?

Steps: 1.Set up a proportion. 2.Solve the proportion. 3.Write the units on the answer.

Example 2 A rectangle shaped dining room table has a length to width ratio of 2:.7. A cover pad is brought to place on the table that will exactly fit its width and length. If the pad is 3.5 feet wide, what will be its length?

Scale Drawings Use the given information and a ruler to make a scale drawing of the object. A chalkboard is 17’ by 14’. Use the scale of 1 cm:2 ft. Steps: 1. Set up a proportions to find the scale measurement of EACH. 2. Solve both proportions.

Scale Drawings (cont.) Steps (cont.) 3. Use a ruler to draw the chalkboard.