1. . . . to use proportions to solve problems involving similar figures.
Today’s Lesson:
What:
similar Figures
Why:
. . . to use proportions to solve problems involving similar figures.

2. What are similar figures ?
Similar figure – figures that are the same shape, but a
different _________.
size
SAME shape!
DIFFERENT size!
CONGRUENT angles!
PROPORTIONAL sides!

3. Identifying corresponding sides . . .WZ WX XY YZ B D

4. Identifying corresponding sides . . .DF EF D E
35°

5. Notice that this is BIG on top and SMALL on bottom!
Solve for a missing side-length:
Trapezoid ABCD is similar to trapezoid
WXYZ (one is a reflection/dilation of the
other). Solve for the missing side-length.
Write corresponding sides as a ratio on each side of the proportion . . .
𝟓 𝟐 =
𝟏𝟐.𝟓 𝐱
5x = 25
Notice that this is BIG on top and SMALL on bottom! 5 5
x = 5 cm

6. Solve for a missing side-length:
Triangle ABC is similar to triangle DEF (one is a rotation/dilation of
the other). Solve for the missing side-length.
Solve for a missing side-length:
x = 5 cm

7. Solve for a missing side-length:
2 Similar Triangles – What is the value of “x”?
x = 19.2 in.

8. Solve for a missing side-length:
A 9.5 ft. tall tree casts a shadow 15 ft. in length. A nearby
building casts a shadow that is 45 ft. in length. How tall is the
building?
x = 28.5 ft.

9. Identifying similar figures . . .
Which triangle below is similar to triangle DEF (circle
your choice) ?
Write given sides on original triangle as a ratio. Then, write the other triangle’s corresponding sides as ratios. Cross-multiply to find out which ratio is equal to original!
ORIGINAL triangle!

10. END OF LESSON