Find Angle B in an Isosceles Trapezoid with 50° Angle

Question

Below is an isosceles trapezoid

If $∢D=50°$

Determine the value of $∢B$ ?

00:00 Find angle B

00:03 According to the given, it's an isosceles trapezoid

00:09 In a trapezoid, angles on the same leg sum to 180

00:23 Let's substitute the value of D to find B

00:34 Let's isolate angle B

00:46 And this is the solution to the question

Let's recall that in an isosceles trapezoid, the sum of the two angles on each of the trapezoid's legs equals 180 degrees.

In other words:

$A+C=180$

$B+D=180$

Since angle D is known to us, we can calculate:

$180-50=B$

$130=B$

130°