Mingmei drew an isosceles triangle on her tablet computer. Only one angle of the triangle measured 70°. Which shows the measures of the other two angles?

A. 60° and 50°
B. 145° and 145°
C. 35° and 75°
D. 55° and 55°

Respuesta :

Answer:

[tex]55^{\circ}[/tex] and [tex]55^{\circ}[/tex].

Step-by-step explanation:

Refer to the diagram attached. In an isosceles triangle ([tex]\triangle {\sf ABC}[/tex],) two of the sides are of equal length (the legs, [tex]{\sf AB}[/tex] and [tex]{\sf AC}[/tex] in the diagram.) The two angles adjacent to the third side (the base, [tex]{\sf BC}[/tex]) would be equal: [tex]\angle {\sf B} = \angle {\sf C}[/tex].

In this question, it is given that only one of the three angles measured [tex]70^{\circ}[/tex]. As the two angles adjacent to the base ([tex]\angle {\sf B}[/tex] and [tex]\angle {\sf C}[/tex]) are of equal measure, this [tex]70^{\circ}[/tex] angle cannot be either of them. Rather, that angle must be opposite to the base: [tex]\angle {\sf A} = 70^{\circ}[/tex].

The sum of the three angles in a triangle should be [tex]180^{\circ}[/tex]. In other words:

[tex]\angle {\sf A} + \angle {\sf B} + \angle {\sf C} = 180^{\circ}[/tex].

Since [tex]\angle {\sf A} = 70^{\circ}[/tex] while [tex]\angle {\sf B} = \angle {\sf C}[/tex]:

[tex]\angle {\sf B} + \angle {\sf C} = 180^{\circ} - 70^{\circ} = 110^{\circ}[/tex].

[tex]\displaystyle \angle {\sf B} = \frac{\angle {\sf B} + \angle {\sf B}}{2} = \frac{\angle {\sf B} + \angle {\sf C}}{2} = \frac{110^{\circ}}{2} = 55^{\circ}[/tex].

[tex]\angle {\sf C} = \angle {\sf B} = 55^{\circ}[/tex].

Hence, the measure of the two other angles would both be [tex]55^{\circ}[/tex].

Ver imagen jacob193