Question

Can someone please explain?

Answer 1

This is an isosceles triangle. The angles at the base are congruent (they have the same measures).

Look at the picture.

We know: The sum of the measures of angles in a triangle is equal 180°.

Therefore we have the equation:

$2x-10+2x-10+3x+25=180$       combine like terms

$(2x+2x+3x)+(-10-10+25)=180$

$7x+5=180$           subtract 5 from both sides

$7x=175$              divide both sides by 7

$x=25$

$m\angle A=2x-10\to m\angle A=2(25)-10=50-10=40\\\\m\angle C=m\angle A=40\\\\m\angle B=3x+25\to m\angle B=3(25)+25=75+25=100^o$

Answer: D. m∠C = 40