Which of the following sets of ordered pairs is not a function? {(-1, 2), (1, 3), (1, 5), (-3, 4)}
{(0, 2), (1, 4), (2, 5), (3, 6)}
{(-4, 3), (-1, 1), (-2, 5), (3, 7)}
{(0, 2), (1, 2), (2, 2), (3, 2)}

Any angle that is visibly smaller than 90° in shape is an acute angle.

Any angle that has a square denoted inside the angle means that it is a 90° angle, therefore implying that it is a right angle.

Any angle that is visibly bigger than 90° in shape is an obtuse angle.

Note that in the Q.8, the total summation of the interior angles for a triangle is  180°. In this case, ∠H & ∠K can be safely assumed to be smaller than right angles, which means that ∠M would be either a right angle or obtuse. However, it is not given that ∠M is a right angle, and so the answer is obtuse.

a. Angle H: acute angle

b. Angle M: obtuse angle

c. Angle K: acute angle

It is given that angles P & T are right angles (as denoted by the squares). Therefore, angle Q & S are obtuse, and angle R is acute, based on visible differences:

a. angle P: Right angle.

b. angle Q: Obtuse angle.

c. angle R: Acute angle.

d. angle S: Obtuse angle.

e. angle T: Right angle.

Usually you will not be using visibility to solve the angle measurements, but in this case, it is not stated that shapes are not drawn to scale. Therefore, you can safely assume based on what the angles look like to answer.