As shown in the figure, △ ABC midpoint D is on BC, and after rotating around point a, △ ABC coincides with △ ace. If ∠ ECB = 100 °, then the rotation angle is?

As shown in the figure, △ ABC midpoint D is on BC, and after rotating around point a, △ ABC coincides with △ ace. If ∠ ECB = 100 °, then the rotation angle is?

After rotation, AB and AC coincide,
∴AB=AC,∴AB=AC=AE,
∴∠ACB=∠ACE=1/2∠ECB=50°,
∴∠BAC=180°-2×50°=80°,
The rotation angle is 80 degrees

In the following triangle, ∠ 1 = ∠ 2, what is the perimeter of this triangle?

Because ∠ 1 = ∠ 2, their opposite sides are also equal, that is, the lengths of the three sides of the triangle are 4cm, 5cm and 5cm respectively, so 4 + 5 + 5 = 14cm; a: the circumference of the triangle is 14cm