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Question

The sides of a triangle are 7,43, and 13 yards respectively. Find the number of degrees in its smallest angle.

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Solution

Let a=7, b=4√3 and c=√13.

In a triangle, the smallest angle has shortest opposite side.

c=√13 is shortest side.

by using cosine formulae

\cos C=\frac{a^2+b^2-c^2}{2ab}

Substitute the given value in the above formula.

\cos C=\frac{(7)^2+(4\sqrt{3})^2-(\sqrt{13})^2}{2(7)(4\sqrt{3})}

\cos C=\frac{49+48-13}{56\sqrt{3}}

\cos C=\frac{84}{56\sqrt{3}}

\cos C=\frac{3}{2\sqrt{3}}

On rationalization.

\cos C=\frac{3\times \sqrt{3}}{2\sqrt{3}\times \sqrt{3}}

\cos C=\frac{3\times \sqrt{3}}{2\times 3}

\cos C=\frac{\sqrt{3}}{2}

\cos C=\cos 30^{\circ}

On comparing both sides.

C=30^{\circ}


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