Given data:
The first angle given is ∠1 =90°.
The second angle given is ∠2 =45°.
The expression for the angle sum property of the triangle is,
[tex]\angle1+\angle2+\angle3=180^{\circ}[/tex]
Substitute the given values in the above expression.
[tex]\begin{gathered} 90^{\circ}+45^{\circ}+\angle3=180^{\circ} \\ \angle3=180^{\circ}-135^{\circ} \\ =45^{\circ} \end{gathered}[/tex]
Thus, the unknown angle is 45 degrees.
