Question

Find the measure of angle C.

Answer 1

`\underset{in~degrees}{\textit{sum of all interior angles}}\\\\ S = 180(n-2) ~~ \begin{cases} n=\stackrel{number~of}{sides}\\[-0.5em] \hrulefill\\ n=4 \end{cases}\implies S=180(4-2)\implies S=360 \\\\[-0.35em] ~\dotfill\\\\ 360 ~~ = ~~ (7x+19)+(15x-1)+(4x-3)+(12x+3) \\\\\\ 360~~ = ~~38x+18\implies 342=38x\implies \cfrac{342}{38}=x\implies \boxed{9=x} \\\\[-0.35em] ~\dotfill\\\\ \stackrel{\measuredangle C}{15x-1}\implies 15(9)-1\implies 135-1\implies \stackrel{\measuredangle C}{\text{\LARGE 134}}`