Chapter 7, Problem 11RP

To determine

To calculate : The value of $m\angle 3$

Answer to Problem 11RP

The value of $m\angle 3={20}^0$

Explanation of Solution

Given information : The following information has been given

An isosceles triangle with base angle equal to ${70}^0$

An altitude is drawn from the vertex

Formula used : The sum of the angles of any triangle is ${180}^0$

Calculation : We know that as one of the angles of the base is ${70}^0$ , the second one will also be ${70}^0$

Now, for an isosceles triangle, the altitude will bisect the vertex

Thus, now we add up the angles of the isosceles triangle, we get

  ${180}^0={70}^0+{70}^0+2\angle 3$

Thus, we get $m\angle 3={20}^0$