The answer that you have is most likely right, since the grouping did not change.
Answer: A
(He has the side lengths in the wrong place in the cosine ratio)
..... 40.5 ...............
Step-by-step explanation:
(3 × 10) × 8 = 3 × (10 × 8)
It's an Associative Property of addition:
<em>(a + b) + c = a + (b + c)</em>
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Check it:
Left side: (3 × 10) × 8 = 30 × 8 = 240
Right side: 3 × (10 × 8) = 3 × 80 = 240
CORRECT
