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Question
If one angle of an isosceles triangle is 70°, then find the possibilities for the other two angles
Solution
(i) Given one angle = 70°
Also, it is an isosceles triangle
Another angle also can be 70°
Sum of these two angles = 70° + 70° = 140°
We know that the sum of three angles in a triangle = 180°
Third angle = 180° – 140° = 40°
One possibility is 70°, 70° and 40°
(ii) Also if one angle is 70°
Sum of other two angles = 180° – 70° = 110°
Both are equal
They are `110/2` = 55°
Another possibility is 70°, 55° and 55°.
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Using the given information, write the type of triangle in the table given below
| S.No | ∠1 | ∠2 | ∠3 | Type of triangle based on angles | Type of triangle based on sides |
| i. | 60° | 40° | 80° | Acute angled triangle. | Scalene Triangle |
| ii. | 50° | 50° | 80° | ||
| iii. | 45° | 45° | 90° | ||
| iv. | 55° | 45° | 80° | ||
| v. | 75° | 35° | 70° | ||
| vi. | 60° | 30° | 90° | ||
| vii. | 25° | 64° | 91° | ||
| viii. | 120° | 30° | 30° |
Is a triangle possible with the angles 90°, 90° and 0°? Why?
State the following statement is true or false? Why?
Every isosceles triangle is an equilateral triangle
Complete the following table:
| Types of Triangle/Its Angles | Acute angled triangle | Right angled triangle | Obtuse angled triangle |
| Any two angles | Always acute angles | i. | Always acute angles |
| Third angle | ii. | Right angle | iii. |
