Question

PLZ HELP

Answer 1

Answer:

The correct option is C ) 109.5°

Therefore,

$m\angle E=109.5\°$

Step-by-step explanation:

Given:

In Triangle DEF

d = 10

e = 18

f = 12

To Find

angle E = ?

Solution:

In Triangle DEF , Cosine Rule says

$\cos E=\dfrac{f^{2}+d^{2}-e^{2}}{2fd}$

Substituting the values we get

$\cos E=\dfrac{12^{2}+10^{2}-18^{2}}{2\times 12\times 10}$

$\cos E=\dfrac{-80}{240}=-\dfrac{1}{3}$

Therefore,

$\angle E=\cos^{-1}(-0.3333)$

$m\angle E=109.5\°$       ............As it is in Second Quadrant

Therefore,

$m\angle E=109.5\°$