Answer:
1. Write the addition of "a", "b" and "c".
2. The equation is: 
Step-by-step explanation:
You know that <em>P</em> represents the perimeter of the triangle and <em>a, b </em>and <em>c </em>represent the sides of the triangle.
By definition, the sum is the result of an addition. Therefore, the statement "The perimeter <em>P</em> of a triangle is equal to the sum of the lengths of sides <em>a, b</em>, and <em>c</em>”, indicates that the perimeter is obtained by adding the lengths of the sides of the triangle.
Knowing this, you can write the following equation:

Answer:
Sin = -5/13
Cos = 12/13
Tan = -5/12
Step-by-step explanation:
The midpoint of 85 and 90 is 87
Answer:
Probability of finding girls given that only English students attend the subject =33/59
Step-by-step explanation:
Given that during English lesson, there is no other lesson ongoing. The probability of getting girls in that class only will be equivalent to 33/59 since we expect a total of 59 students out of which 33 will be girls. Similarly, in a Maths class given that only Maths students attend the class, probability of having a girl is 29/61 since out of all students, only 29 prefer Maths and the total class attendance is 61