If isosceles triangle abc has a 130° angle at vertex b, which statement must be true?
m∠a = 15° and m∠c = 35°
m∠a + m∠b = 155°
m∠a + m∠c = 60°
m∠a = 20° and m∠c = 30°.

Step-by-step explanation:

2 angles of same length

all angles in a triangle add to 180

so

if the angles are m∠A, m∠B, m∠C, then

either m∠A=m∠B or m∠B=m∠C or m∠A=m∠C

anyway

so if we assume that vertex B is the one that has a twin then

130+130+?=180

260+?=180

?=-80

false, we can't have a negative angle measure

so 130 must be the odd one

?+?+130=180

2?+130=180

2?=50

?=25

so

m∠A=m∠C=25°

let's test the 2nd answer choice

m∠A+m∠B=25+130=155, yep

test 3rd

m∠A+m∠C=25+25=50≠60, nope

not 3rd one

so answer is 2nd statement

m∠A+ m∠B = 155°

b is 38 degrees.

a is 52 degrees.

this is because if b is 38 and a is 14 degrees more than b than 38+14=52 and 52+38=90 degrees. hope this .