Consider the following sets.

u = {all triangles}

e = {x|x ∈ u and x is equilateral}
i = {x|x ∈ u and x is isosceles}
s = {x|x ∈ u and x is scalene}
a = {x|x ∈ u and x is acute}
o = {x|x ∈ u and x is obtuse}
r = {x|x ∈ u and x is right

which is a subset of i?

e
s
a
r

Option 1 is correct that is  e={x|x∈ u and x is equilateral}

Step-by-step explanation:

We have been given i={x|x∈ u and x is isosceles}

Isosceles triangle is the one in which two sides are equal

So, Option 1 that is e={x|x∈ u and x is equilateral} is correct because equilateral triangle is the triangle which has three of its sides equal.

Rest of the options are incorrect.

Sometimes right angle triangle has two sides equal but not always.

expression #3 is not equivalent. the others are.