9. 471.7 square units
10. 827.0 square units
<h3>Explanation:</h3>If you're going to have someone else solve your problem for you, it is much quicker and easier to use an appropriate computer or graphing calculator app. (See the attached.)
9. There are at least a couple of ways to approach this. The law of sines can be used to find the length of another side. Given two sides and the angle between them, a formula gives area.
<em>Law of Sines</em>
... a/sin(A) = c/sin(C)
Multiplying by sin(C) gives
... c = sin(C)·a/sin(A) = 19·sin(64°)/sin(20°) ≈ 49.9301
The angle between sides a and c is B, which has the value ...
... B = 180° -A -C = 180° -20° -64° = 96°
Then the area of the triangle is ...
... Area = (1/2)ac·sin(B) = (1/2)(19)(49.9301)(0.994522) ≈ 471.737 ≈ 471.7
10. Heron's formula will give the area of a triangle from its side lengths.
... s = (a+b+c)/2 = (51+38+45)/2 = 67
... Area = √(s(s-a)(s-b)(s-c)) = √(67·16·29·22) = √683936 ≈ 827.004 ≈ 827.0
