You have to use the Law of Cosines here, since there's no other way to solve this. it's not a right triangle, so you can't use the Pythagorean Theorem. The Law of Cosines will help us find the missing side length then we will have to use the Law of Sines to find another angle. Then after that we will use the Triangle Angle-Sum theorem to finish it off. Ready? The Law of Cosines to find side b is
and fill in the info we know, which is everything but the b. 
. Doing all that math gives us that side b = 40.9 or 41. Now the Law of Sines to find missing angle A or C. Let's find A. 
. That gives us that angle A is 29. Now use the fact that all triangles add up to 180 to get that angle C is 42. And you're done!
Find the proportion of the missing number 7/a = 2/4
1 answer:
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Answer:
See explanation
Step-by-step explanation:
If then triangle PXY is isosceles triangle. Angles adjacent to the base XY of an isosceles triangle PXY are congruent, so
and
Angles 1 and 3 are supplementary, so
Angles 2 and 4 are supplementary, so
By substitution property,
Hence,
Consider triangles APX and BPY. In these triangles:
- given;
- given;
- proven,
so by ASA postulate.
Congruent triangles have congruent corresponding sides, then
Therefore, triangle APB is isosceles triangle (by definition).