In ΔLMN, l = 8.7 cm, m = 2.3 cm and n=6.6 cm. Find the measure of ∠M to the nearest degree.

7

Step-by-step explanation:

\underline{\text{Solution Method 2:}}

Solution Method 2:

Use original formula

a^2=b^2+c^2-2bc\cos A

a

2

=b

2

+c

2

−2bccosA

From reference sheet.

\text{Since we are finding }\angle M\text{,}

Since we are finding ∠M,

\text{plug in }2.3\text{ for side }a:

plug in 2.3 for side a:

Opposit the angle we want

2.3^2 = 6.6^2+8.7^2-2(6.6)(8.7)\cos M

2.3

2

=6.6

2

+8.7

2

−2(6.6)(8.7)cosM

Plug in values. Side "a" is opposite the wanted angle.

5.29 = 43.56+75.69-114.84\cos M

5.29=43.56+75.69−114.84cosM

Square sides.

5.29 =

5.29=

\,\,\color{white}{-} 119.25-114.84\cos M

−119.25−114.84cosM

Add.

-119.25=

−119.25=

\,\,-119.25

−119.25

-113.96=

−113.96=

\,\,-114.84\cos M

−114.84cosM

\frac{-113.96}{-114.84}=\cos M

−114.84

−113.96

=cosM

Divide to solve for cos(A).

M= \cos^{-1}(\frac{-113.96}{-114.84})\approx7.098\approx 7^{\circ}

M=cos

−1

(

−114.84

−113.96

)≈7.098≈7

∘