Answer:
The answer is:
[tex]\bold{c\approx 20.2\ units}[/tex]
Step-by-step explanation:
Given:
In △ABC:
m∠A=15°
a=10 and
b=11
To find:
c = ?
Solution:
We can use cosine rule here to find the value of third side c.
Formula for cosine rule:
[tex]cos A = \dfrac{b^{2}+c^{2}-a^{2}}{2bc}[/tex]
Where
a is the side opposite to [tex]\angle A[/tex]
b is the side opposite to [tex]\angle B[/tex]
c is the side opposite to [tex]\angle C[/tex]
Putting all the values.
[tex]cos 15^\circ = \dfrac{11^{2}+c^{2}-10^{2}}{2\times 11 \times c}\\\Rightarrow 0.96 = \dfrac{121+c^{2}-100}{22c}\\\Rightarrow 0.96 \times 22c= 121+c^{2}-100\\\Rightarrow 21.25 c= 21+c^{2}\\\Rightarrow c^{2}-21.25c+21=0\\\\\text{solving the quadratic equation:}\\\\c = \dfrac{21.25+\sqrt{21.25^2-4 \times 1 \times 21}}{2}\\c = \dfrac{21.25+\sqrt{367.56}}{2}\\c = \dfrac{21.25+19.17}{2}\\c \approx 20.2\ units[/tex]
The answer is:
[tex]\bold{c\approx 20.2\ units}[/tex]
