Suppose a triangle has sides a, b, and c, and that a2 + b2 < c2. let be the measure of the angle opposite the side of length c. which of the following must be true? check all that apply.
a. cosθ < 0
b. the triangle is a right triangle
c. the triangle is not a right triangle
d. θ is an obtuse angle

A.

B.The triangle is not a right triangle

C. is an obtuse angle

Step-by-step explanation:

We are given that a triangle with sides a, b and c.

When a triangle is an obtuse triangle then

It means given triangle is an obtuse triangle .

Obtuse triangle is that triangle in which one angle is an obtuse angle.

Let be the measure of angle opposite the side of length c.

We have to find the statements which are must be true.

Cosine law:

Substitute the value then we get  

Subtracting on both sides of inequality  

Adding on both sides then we get

is negative in second quadrant and third quadrant.

Therefore,

But, we know that an obtuse angle is that angle which is greater than 90 degrees and less than 180 degrees.

Hence,

Option A ,C and D are true.