The equation which is correctly used the law of cosines to solve for the length of [tex]s[/tex] is
[tex]s^2 = 9^2 +10^2 - 2(9)(10)\cos(100^o)[/tex]
Thus the option 4 is the correct option.
What is law of cosine?
The law of cosine is the nothing but the relationship between the sides of the triangle to the angle of the triangle (oblique triangle).
It can be given as,
[tex]a^2=b^2+c^2-2bc\cos(A)[/tex]
Here [tex]A[/tex] is the angle of the triangle and [tex]a,b,c[/tex] are the sides of that triangle.
Given information-
The side of the triangle is [tex]s[/tex].
The angle of the side [tex]s[/tex] is 100 degrees.
The measure of the other two side are 9 units and 10 units.
The image attached below for the given problem.
Compare with the cosine law written above we get,
[tex]a=s\\b=9\\c=10\\m\angle A=m\angle S=100[/tex]
Put the values in the cosine law as,
[tex]s^2 = 9^2 +10^2 - 2(9)(10)\cos(100^o)[/tex]
Hence the equation which is correctly used the law of cosines to solve for the length of [tex]s[/tex] is
[tex]s^2 = 9^2 +10^2 - 2(9)(10)\cos(100^o)[/tex]
Thus the option 4 is the correct option.
Learn more about the cosine law here;
https://brainly.com/question/4372174
