9514 1404 393
Answer:
18 cm^2
Step-by-step explanation:
Under the given constraints, the way to find the area of this triangle is to use a triangle solver app or web site. The attached shows the area is 18 cm^2.
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A simple way to find the area is to use the cosine function to find side AC adjacent to the 75° angle. Then use the formula for area that uses the sine function.
AC = AB·cos(75°)
Area = (1/2)AB·AC·sin(75°)
Area = (1/2)(AB²)cos(75)sin(75°)
= (1/4)AB²·sin(150°) . . . using the double-angle identity
= (1/4)(12 cm)²(1/2)
Area = 18 cm²
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The useful relations are ...
Cos = Adjacent/Hypotenuse
cos(75°) = AC/AB ⇒ AC = AB·cos(75°)
and ...
Area = (1/2)pq·sin(α) . . . . for two sides p and q with angle α between them
Area = (1/2)AB·AC·sin(75°)
Another identity we used here is ...
sin(2α) = 2sin(α)cos(α) ⇔ sin(α)cos(α) = (1/2)sin(2α)
Putting these together, the formula for area we used was effectively ...
A = (1/4)AB²sin(2·75°)
