7 x 13 = 91.......so 91 is not a prime, it is a composite
Given:
Sides of triangles in the options.
To find:
Which could NOT be the lengths of the sides of a triangle.
Solution:
Condition for triangle:
Sum of two smaller sides of a triangle must be greater than the longest side.
In option A,

Sides 5 in, 5 in, 5 in are the lengths of the sides of a triangle.
In option B,

Sides 10 cm, 15 cm, 20 cm are the lengths of the sides of a triangle.
In option C,

Sides 3 in, 4 in, 5 in are the lengths of the sides of a triangle.
In option D,

Since, the sum of two smaller sides is less than the longest side, therefore the sides 8 ft, 15 ft, 5 ft are not the lengths of the sides of a triangle.
Therefore, the correct option is D.
Answer:
9
Step-by-step explanation:
sorry if wrong
X = 5
So 3x = 3(5) = 15
3x = 15
Answer:
-3.53553390593
Step-by-step explanation:
5(cos165-cos105)=-3.53553390593