What type of triangle is formed by joining the points d(7, 3), e(8, 1), and
f(4, -1)?

DEF is a right angle triangle.

Step-by-step explanation:

Given: Three coordinate of triangle.  D(7, 3), E(8, 1), and  F(4, -1)

Using distance formula to find the length of side of triangle.

DE≠DF≠EF

Thus, DEF is neither equilateral nor isosceles.

Using pythagoreous theorem,

LHS  = RHS

So, Triangle DEF is satisfy the pythagoreous theorem.

Thus, DEF is a right angle triangle.

1/4 because there is 4 grades.