The equation that correctly uses the law of cosines to solve for the missing side length of trianglepqr is 8^2 = 7^2 +11^2 - 2(7)(11) cos <P
For us to use the cosine formula, an angle must be situated between two sides of the triangle.
According to the rule;
c^2 = a^2 + b^2 - 2ab cos C
From the given diagram, if cos<P is the reference angle, then;
a = 11
b = 7
c = 8
Substiute
8^2 = 7^2 +11^2 - 2(7)(11) cos <P
Hence the equation that correctly uses the law of cosines to solve for the missing side length of trianglepqr is 8^2 = 7^2 +11^2 - 2(7)(11) cos <P
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