Lesson
[Definition]
Isosceles Triangles
An isosceles triangle has two equal sides and two equal base angles
Example
Match the numbered statements in Column X with the letters allocated to the diagrams in Column Y by classifying according to sides or angles.
Explain your answers.
听Column X
|
听Column Y
|
||
1 |
听 An acute triangle has 3 acute angles |
A |
|
| 2 |
A right triangle has 1 right angle |
B | |
| 3 |
An obtuse triangle has 1 obtuse angle |
C |
|
| 4 |
听 An equilateral triangle has 3 congruent sides听听 |
D | |
| 5 |
听 An isosceles triangle has at least 2 congruent sides听听 |
E |
|
| 6 |
A scalene triangle has no sides of equal length |
F | |
听
Solution
|
听 1-E 听 All angles are less than 90掳听 |
听 2-A 听 One angles is equal to 90掳听 |
听 3-B 听 One angle is greater than 90掳听 |
|
听 4-C 听All sides are of equal length |
听 5-F 听 Two sides are of equal length |
听 6-D 听 None of the sides are equal length听听 |
Question
A triangle鈥檚 largest angle is 2.5 times larger than the smallest angle. If the third angle is 40掳, what type of triangle is it?
听
Explanation
Given the information, we can create an equation and solve.
2.5x + x +40 = 180
3.5x = 140
x = 40
Therefore, the angles are 100掳, 40掳, 40掳 and the triangle is isosceles.
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