Question

For triangle ABC, a = 79, b = 68, c = 61, then M∠A= ___ °Round answer to one decimal place.

Answer 1

Given a triangle ABC below

To find the value of m∠A, we use the cosine formula which is

`\cos A=(b^2+c^2-a^2)/(2bc)`

Where

`\begin{gathered} a=79 \\ b=68 \\ c=61 \end{gathered}`

Substitute the values into the cosine formula above

`\begin{gathered} \cos A=(b^2+c^2-a^2)/(2bc) \\ \cos A=(68^2+61^2-79^2)/(2(68)(61)) \\ \cos A=(2104)/(8296) \\ \cos A=0.2536 \\ A=\cos ^(-1)(0.2536) \\ A=75.3\degree\text{ (one decimal place)} \end{gathered}`

Hence, m∠A is 75.3° (one decimal place)