In ∆DEF, DE = 18, EF = 16, and DF = 12. Find m∠F.
1 answer:
Answer:
∠F=78.58484226°
Step-by-step explanation:
a²=b²+c² - 2bc cosA
DE²=EF²+DF² - 2(EF)(DF)cos∠F
18²=16²+12²-2(16)(12)cos∠F
324=256+144-384cos∠F
324-400=-384cos∠F
76=384cos∠F
0.197916=cos∠F
∠F=cos⁻¹(0.197916)
∠F=78.58484226°
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