We are given a triangle $\triangle ABC$. A line segment $BD$ is perpendicular to $AC$ at point D ($BD \perp AC$). We know the angle $\angle DBC = 71^\circ$. Another point E lies on the side BC, and we are given $\angle CAE = 17^\circ$. The goal is to find the measure of the angle $\angle AEB$.
Consider the triangle $\triangle BDC$. Since $BD \perp AC$, the angle $\angle BDC$ is a right angle ($90^\circ$). The sum of angles in any triangle is $180^\circ$. In $\triangle BDC$, we have:
Using the angle sum property:
$ \angle BCA = 180^\circ - \angle BDC - \angle DBC $
$ \angle BCA = 180^\circ - 90^\circ - 71^\circ $
$ \angle BCA = 19^\circ $
Since point E lies on BC, $\angle ACE$ is the same angle, so $\angle ACE = 19^\circ$.
Let's denote the angle $\angle BAE$ as $\alpha$.
The angle $\angle BAC$ is the sum of $\angle BAE$ and $\angle CAE$:
$ \angle BAC = \angle BAE + \angle CAE $
$ \angle BAC = \alpha + 17^\circ $
Now, consider the larger triangle $\triangle ABC$. The sum of its angles must be $180^\circ$. We can find $\angle ABC$:
$ \angle ABC = 180^\circ - \angle BAC - \angle BCA $
Substitute the expressions for $\angle BAC$ and the value of $\angle BCA$:
$ \angle ABC = 180^\circ - (\alpha + 17^\circ) - 19^\circ $
$ \angle ABC = 180^\circ - \alpha - 17^\circ - 19^\circ $
$ \angle ABC = 180^\circ - \alpha - 36^\circ $
$ \angle ABC = 144^\circ - \alpha $
Since E is on BC, $\angle ABE$ is the same as $\angle ABC$. So, $\angle ABE = 144^\circ - \alpha$.
Finally, apply the angle sum property to triangle $\triangle ABE$:
$ \angle BAE + \angle ABE + \angle AEB = 180^\circ $
Substitute the known values and expressions:
$ \alpha + (144^\circ - \alpha) + \angle AEB = 180^\circ $
The $\alpha$ terms cancel out:
$ 144^\circ + \angle AEB = 180^\circ $
Solve for $\angle AEB$:
$ \angle AEB = 180^\circ - 144^\circ $
$ \angle AEB = 36^\circ $
The measure of angle $\angle AEB$ is $36^\circ$.
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